1313 lines
54 KiB
Markdown
1313 lines
54 KiB
Markdown
terser
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======
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A JavaScript parser and mangler/compressor toolkit for ES6+.
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*note*: You can support this project on patreon: <a target="_blank" rel="nofollow" href="https://www.patreon.com/fabiosantoscode"><img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" alt="patron" width="100px" height="auto"></a>. Check out [PATRONS.md](https://github.com/terser-js/terser/blob/master/PATRONS.md) for our first-tier patrons.
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Terser recommends you use RollupJS to bundle your modules, as that produces smaller code overall.
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*Beautification* has been undocumented and is *being removed* from terser, we recommend you use [prettier](https://npmjs.com/package/prettier).
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[](https://travis-ci.org/terser-js/terser)
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Find the changelog in [CHANGELOG.md](https://github.com/terser-js/terser/blob/master/CHANGELOG.md)
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A JavaScript parser, mangler/compressor and beautifier toolkit for ES6+.
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Why choose terser?
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------------------
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`uglify-es` is [no longer maintained](https://github.com/mishoo/UglifyJS2/issues/3156#issuecomment-392943058) and `uglify-js` does not support ES6+.
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**`terser`** is a fork of `uglify-es` that mostly retains API and CLI compatibility
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with `uglify-es` and `uglify-js@3`.
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Install
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-------
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First make sure you have installed the latest version of [node.js](http://nodejs.org/)
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(You may need to restart your computer after this step).
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From NPM for use as a command line app:
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npm install terser -g
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From NPM for programmatic use:
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npm install terser
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# Command line usage
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terser [input files] [options]
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Terser can take multiple input files. It's recommended that you pass the
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input files first, then pass the options. Terser will parse input files
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in sequence and apply any compression options. The files are parsed in the
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same global scope, that is, a reference from a file to some
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variable/function declared in another file will be matched properly.
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If no input file is specified, Terser will read from STDIN.
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If you wish to pass your options before the input files, separate the two with
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a double dash to prevent input files being used as option arguments:
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terser --compress --mangle -- input.js
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### Command line options
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```
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-h, --help Print usage information.
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`--help options` for details on available options.
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-V, --version Print version number.
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-p, --parse <options> Specify parser options:
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`acorn` Use Acorn for parsing.
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`bare_returns` Allow return outside of functions.
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Useful when minifying CommonJS
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modules and Userscripts that may
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be anonymous function wrapped (IIFE)
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by the .user.js engine `caller`.
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`expression` Parse a single expression, rather than
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a program (for parsing JSON).
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`spidermonkey` Assume input files are SpiderMonkey
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AST format (as JSON).
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-c, --compress [options] Enable compressor/specify compressor options:
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`pure_funcs` List of functions that can be safely
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removed when their return values are
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not used.
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-m, --mangle [options] Mangle names/specify mangler options:
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`reserved` List of names that should not be mangled.
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--mangle-props [options] Mangle properties/specify mangler options:
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`builtins` Mangle property names that overlaps
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with standard JavaScript globals.
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`debug` Add debug prefix and suffix.
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`domprops` Mangle property names that overlaps
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with DOM properties.
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`keep_quoted` Only mangle unquoted properties, quoted
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properties are automatically reserved.
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`strict` disables quoted properties
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being automatically reserved.
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`regex` Only mangle matched property names.
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`reserved` List of names that should not be mangled.
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-b, --beautify [options] Specify output options:
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`preamble` Preamble to prepend to the output. You
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can use this to insert a comment, for
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example for licensing information.
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This will not be parsed, but the source
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map will adjust for its presence.
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`quote_style` Quote style:
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0 - auto
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1 - single
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2 - double
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3 - original
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`wrap_iife` Wrap IIFEs in parenthesis. Note: you may
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want to disable `negate_iife` under
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compressor options.
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-o, --output <file> Output file path (default STDOUT). Specify `ast` or
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`spidermonkey` to write Terser or SpiderMonkey AST
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as JSON to STDOUT respectively.
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--comments [filter] Preserve copyright comments in the output. By
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default this works like Google Closure, keeping
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JSDoc-style comments that contain "@license" or
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"@preserve". You can optionally pass one of the
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following arguments to this flag:
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- "all" to keep all comments
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- a valid JS RegExp like `/foo/` or `/^!/` to
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keep only matching comments.
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Note that currently not *all* comments can be
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kept when compression is on, because of dead
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code removal or cascading statements into
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sequences.
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--config-file <file> Read `minify()` options from JSON file.
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-d, --define <expr>[=value] Global definitions.
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--ecma <version> Specify ECMAScript release: 5, 6, 7 or 8.
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-e, --enclose [arg[:value]] Embed output in a big function with configurable
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arguments and values.
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--ie8 Support non-standard Internet Explorer 8.
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Equivalent to setting `ie8: true` in `minify()`
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for `compress`, `mangle` and `output` options.
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By default Terser will not try to be IE-proof.
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--keep-classnames Do not mangle/drop class names.
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--keep-fnames Do not mangle/drop function names. Useful for
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code relying on Function.prototype.name.
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--module Input is an ES6 module. If `compress` or `mangle` is
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enabled then the `toplevel` option will be enabled.
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--name-cache <file> File to hold mangled name mappings.
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--safari10 Support non-standard Safari 10/11.
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Equivalent to setting `safari10: true` in `minify()`
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for `mangle` and `output` options.
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By default `terser` will not work around
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Safari 10/11 bugs.
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--source-map [options] Enable source map/specify source map options:
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`base` Path to compute relative paths from input files.
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`content` Input source map, useful if you're compressing
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JS that was generated from some other original
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code. Specify "inline" if the source map is
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included within the sources.
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`filename` Name and/or location of the output source.
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`includeSources` Pass this flag if you want to include
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the content of source files in the
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source map as sourcesContent property.
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`root` Path to the original source to be included in
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the source map.
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`url` If specified, path to the source map to append in
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`//# sourceMappingURL`.
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--timings Display operations run time on STDERR.
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--toplevel Compress and/or mangle variables in top level scope.
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--verbose Print diagnostic messages.
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--warn Print warning messages.
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--wrap <name> Embed everything in a big function, making the
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“exports” and “global” variables available. You
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need to pass an argument to this option to
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specify the name that your module will take
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when included in, say, a browser.
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```
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Specify `--output` (`-o`) to declare the output file. Otherwise the output
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goes to STDOUT.
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## CLI source map options
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Terser can generate a source map file, which is highly useful for
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debugging your compressed JavaScript. To get a source map, pass
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`--source-map --output output.js` (source map will be written out to
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`output.js.map`).
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Additional options:
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- `--source-map "filename='<NAME>'"` to specify the name of the source map.
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- `--source-map "root='<URL>'"` to pass the URL where the original files can be found.
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- `--source-map "url='<URL>'"` to specify the URL where the source map can be found.
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Otherwise Terser assumes HTTP `X-SourceMap` is being used and will omit the
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`//# sourceMappingURL=` directive.
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For example:
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terser js/file1.js js/file2.js \
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-o foo.min.js -c -m \
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--source-map "root='http://foo.com/src',url='foo.min.js.map'"
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The above will compress and mangle `file1.js` and `file2.js`, will drop the
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output in `foo.min.js` and the source map in `foo.min.js.map`. The source
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mapping will refer to `http://foo.com/src/js/file1.js` and
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`http://foo.com/src/js/file2.js` (in fact it will list `http://foo.com/src`
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as the source map root, and the original files as `js/file1.js` and
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`js/file2.js`).
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### Composed source map
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When you're compressing JS code that was output by a compiler such as
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CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd
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like to map back to the original code (i.e. CoffeeScript). Terser has an
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option to take an input source map. Assuming you have a mapping from
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CoffeeScript → compiled JS, Terser can generate a map from CoffeeScript →
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compressed JS by mapping every token in the compiled JS to its original
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location.
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To use this feature pass `--source-map "content='/path/to/input/source.map'"`
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or `--source-map "content=inline"` if the source map is included inline with
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the sources.
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## CLI compress options
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You need to pass `--compress` (`-c`) to enable the compressor. Optionally
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you can pass a comma-separated list of [compress options](#compress-options).
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Options are in the form `foo=bar`, or just `foo` (the latter implies
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a boolean option that you want to set `true`; it's effectively a
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shortcut for `foo=true`).
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Example:
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terser file.js -c toplevel,sequences=false
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## CLI mangle options
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To enable the mangler you need to pass `--mangle` (`-m`). The following
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(comma-separated) options are supported:
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- `toplevel` (default `false`) -- mangle names declared in the top level scope.
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- `eval` (default `false`) -- mangle names visible in scopes where `eval` or `with` are used.
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When mangling is enabled but you want to prevent certain names from being
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mangled, you can declare those names with `--mangle reserved` — pass a
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comma-separated list of names. For example:
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terser ... -m reserved=['$','require','exports']
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to prevent the `require`, `exports` and `$` names from being changed.
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### CLI mangling property names (`--mangle-props`)
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**Note:** THIS **WILL** BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end.
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Mangling property names is a separate step, different from variable name mangling. Pass
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`--mangle-props` to enable it. The least dangerous
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way to use this is to use the `regex` option like so:
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```
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terser example.js -c -m --mangle-props regex=/_$/
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```
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This will mangle all properties that start with an
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underscore. So you can use it to mangle internal methods.
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By default, it will mangle all properties in the
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input code with the exception of built in DOM properties and properties
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in core JavaScript classes, which is what will break your code if you don't:
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1. Control all the code you're mangling
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2. Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules.
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3. Avoid calling functions like `defineProperty` or `hasOwnProperty`, because they refer to object properties using strings and will break your code if you don't know what you are doing.
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An example:
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```javascript
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// example.js
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var x = {
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baz_: 0,
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foo_: 1,
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calc: function() {
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return this.foo_ + this.baz_;
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}
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};
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x.bar_ = 2;
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x["baz_"] = 3;
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console.log(x.calc());
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```
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Mangle all properties (except for JavaScript `builtins`) (**very** unsafe):
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```bash
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$ terser example.js -c -m --mangle-props
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```
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```javascript
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var x={o:0,_:1,l:function(){return this._+this.o}};x.t=2,x.o=3,console.log(x.l());
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```
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Mangle all properties except for `reserved` properties (still very unsafe):
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```bash
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$ terser example.js -c -m --mangle-props reserved=[foo_,bar_]
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```
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```javascript
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var x={o:0,foo_:1,_:function(){return this.foo_+this.o}};x.bar_=2,x.o=3,console.log(x._());
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```
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Mangle all properties matching a `regex` (not as unsafe but still unsafe):
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```bash
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$ terser example.js -c -m --mangle-props regex=/_$/
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```
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```javascript
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var x={o:0,_:1,calc:function(){return this._+this.o}};x.l=2,x.o=3,console.log(x.calc());
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```
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Combining mangle properties options:
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```bash
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$ terser example.js -c -m --mangle-props regex=/_$/,reserved=[bar_]
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```
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```javascript
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var x={o:0,_:1,calc:function(){return this._+this.o}};x.bar_=2,x.o=3,console.log(x.calc());
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```
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In order for this to be of any use, we avoid mangling standard JS names by
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default (`--mangle-props builtins` to override).
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A default exclusion file is provided in `tools/domprops.json` which should
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cover most standard JS and DOM properties defined in various browsers. Pass
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`--mangle-props domprops` to disable this feature.
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A regular expression can be used to define which property names should be
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mangled. For example, `--mangle-props regex=/^_/` will only mangle property
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names that start with an underscore.
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When you compress multiple files using this option, in order for them to
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work together in the end we need to ensure somehow that one property gets
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mangled to the same name in all of them. For this, pass `--name-cache filename.json`
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and Terser will maintain these mappings in a file which can then be reused.
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It should be initially empty. Example:
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```bash
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$ rm -f /tmp/cache.json # start fresh
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$ terser file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
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$ terser file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js
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```
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Now, `part1.js` and `part2.js` will be consistent with each other in terms
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of mangled property names.
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Using the name cache is not necessary if you compress all your files in a
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single call to Terser.
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### Mangling unquoted names (`--mangle-props keep_quoted`)
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Using quoted property name (`o["foo"]`) reserves the property name (`foo`)
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so that it is not mangled throughout the entire script even when used in an
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unquoted style (`o.foo`). Example:
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```javascript
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// stuff.js
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var o = {
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"foo": 1,
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bar: 3
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};
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o.foo += o.bar;
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console.log(o.foo);
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```
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```bash
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$ terser stuff.js --mangle-props keep_quoted -c -m
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```
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```javascript
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var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo);
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```
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### Debugging property name mangling
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You can also pass `--mangle-props debug` in order to mangle property names
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without completely obscuring them. For example the property `o.foo`
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would mangle to `o._$foo$_` with this option. This allows property mangling
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of a large codebase while still being able to debug the code and identify
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where mangling is breaking things.
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```bash
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$ terser stuff.js --mangle-props debug -c -m
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```
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```javascript
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var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_);
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```
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You can also pass a custom suffix using `--mangle-props debug=XYZ`. This would then
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mangle `o.foo` to `o._$foo$XYZ_`. You can change this each time you compile a
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script to identify how a property got mangled. One technique is to pass a
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random number on every compile to simulate mangling changing with different
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inputs (e.g. as you update the input script with new properties), and to help
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identify mistakes like writing mangled keys to storage.
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# API Reference
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Assuming installation via NPM, you can load Terser in your application
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like this:
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```javascript
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var Terser = require("terser");
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```
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Browser loading is also supported:
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```html
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<script src="node_modules/source-map/dist/source-map.min.js"></script>
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<script src="dist/bundle.min.js"></script>
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```
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There is a single high level function, **`minify(code, options)`**,
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which will perform all minification [phases](#minify-options) in a configurable
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manner. By default `minify()` will enable the options [`compress`](#compress-options)
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and [`mangle`](#mangle-options). Example:
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```javascript
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var code = "function add(first, second) { return first + second; }";
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var result = Terser.minify(code);
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console.log(result.error); // runtime error, or `undefined` if no error
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console.log(result.code); // minified output: function add(n,d){return n+d}
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```
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You can `minify` more than one JavaScript file at a time by using an object
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for the first argument where the keys are file names and the values are source
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code:
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```javascript
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var code = {
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"file1.js": "function add(first, second) { return first + second; }",
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"file2.js": "console.log(add(1 + 2, 3 + 4));"
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};
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var result = Terser.minify(code);
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console.log(result.code);
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// function add(d,n){return d+n}console.log(add(3,7));
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```
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The `toplevel` option:
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```javascript
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var code = {
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"file1.js": "function add(first, second) { return first + second; }",
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"file2.js": "console.log(add(1 + 2, 3 + 4));"
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};
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var options = { toplevel: true };
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var result = Terser.minify(code, options);
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console.log(result.code);
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// console.log(3+7);
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```
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The `nameCache` option:
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```javascript
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var options = {
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mangle: {
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toplevel: true,
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},
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nameCache: {}
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};
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var result1 = Terser.minify({
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"file1.js": "function add(first, second) { return first + second; }"
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}, options);
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var result2 = Terser.minify({
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"file2.js": "console.log(add(1 + 2, 3 + 4));"
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}, options);
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console.log(result1.code);
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// function n(n,r){return n+r}
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console.log(result2.code);
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// console.log(n(3,7));
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```
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You may persist the name cache to the file system in the following way:
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```javascript
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var cacheFileName = "/tmp/cache.json";
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var options = {
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mangle: {
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properties: true,
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},
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nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8"))
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};
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fs.writeFileSync("part1.js", Terser.minify({
|
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"file1.js": fs.readFileSync("file1.js", "utf8"),
|
|
"file2.js": fs.readFileSync("file2.js", "utf8")
|
|
}, options).code, "utf8");
|
|
fs.writeFileSync("part2.js", Terser.minify({
|
|
"file3.js": fs.readFileSync("file3.js", "utf8"),
|
|
"file4.js": fs.readFileSync("file4.js", "utf8")
|
|
}, options).code, "utf8");
|
|
fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8");
|
|
```
|
|
|
|
An example of a combination of `minify()` options:
|
|
```javascript
|
|
var code = {
|
|
"file1.js": "function add(first, second) { return first + second; }",
|
|
"file2.js": "console.log(add(1 + 2, 3 + 4));"
|
|
};
|
|
var options = {
|
|
toplevel: true,
|
|
compress: {
|
|
global_defs: {
|
|
"@console.log": "alert"
|
|
},
|
|
passes: 2
|
|
},
|
|
output: {
|
|
beautify: false,
|
|
preamble: "/* minified */"
|
|
}
|
|
};
|
|
var result = Terser.minify(code, options);
|
|
console.log(result.code);
|
|
// /* minified */
|
|
// alert(10);"
|
|
```
|
|
|
|
To produce warnings:
|
|
```javascript
|
|
var code = "function f(){ var u; return 2 + 3; }";
|
|
var options = { warnings: true };
|
|
var result = Terser.minify(code, options);
|
|
console.log(result.error); // runtime error, `undefined` in this case
|
|
console.log(result.warnings); // [ 'Dropping unused variable u [0:1,18]' ]
|
|
console.log(result.code); // function f(){return 5}
|
|
```
|
|
|
|
An error example:
|
|
```javascript
|
|
var result = Terser.minify({"foo.js" : "if (0) else console.log(1);"});
|
|
console.log(JSON.stringify(result.error));
|
|
// {"message":"Unexpected token: keyword (else)","filename":"foo.js","line":1,"col":7,"pos":7}
|
|
```
|
|
Note: unlike `uglify-js@2.x`, the Terser API does not throw errors.
|
|
To achieve a similar effect one could do the following:
|
|
```javascript
|
|
var result = Terser.minify(code, options);
|
|
if (result.error) throw result.error;
|
|
```
|
|
|
|
## Minify options
|
|
|
|
- `ecma` (default `undefined`) - pass `5`, `6`, `7` or `8` to override `parse`,
|
|
`compress` and `output` options.
|
|
|
|
- `warnings` (default `false`) — pass `true` to return compressor warnings
|
|
in `result.warnings`. Use the value `"verbose"` for more detailed warnings.
|
|
|
|
- `parse` (default `{}`) — pass an object if you wish to specify some
|
|
additional [parse options](#parse-options).
|
|
|
|
- `compress` (default `{}`) — pass `false` to skip compressing entirely.
|
|
Pass an object to specify custom [compress options](#compress-options).
|
|
|
|
- `mangle` (default `true`) — pass `false` to skip mangling names, or pass
|
|
an object to specify [mangle options](#mangle-options) (see below).
|
|
|
|
- `mangle.properties` (default `false`) — a subcategory of the mangle option.
|
|
Pass an object to specify custom [mangle property options](#mangle-properties-options).
|
|
|
|
- `module` (default `false`) — Use when minifying an ES6 module. "use strict"
|
|
is implied and names can be mangled on the top scope. If `compress` or
|
|
`mangle` is enabled then the `toplevel` option will be enabled.
|
|
|
|
- `output` (default `null`) — pass an object if you wish to specify
|
|
additional [output options](#output-options). The defaults are optimized
|
|
for best compression.
|
|
|
|
- `sourceMap` (default `false`) - pass an object if you wish to specify
|
|
[source map options](#source-map-options).
|
|
|
|
- `toplevel` (default `false`) - set to `true` if you wish to enable top level
|
|
variable and function name mangling and to drop unused variables and functions.
|
|
|
|
- `nameCache` (default `null`) - pass an empty object `{}` or a previously
|
|
used `nameCache` object if you wish to cache mangled variable and
|
|
property names across multiple invocations of `minify()`. Note: this is
|
|
a read/write property. `minify()` will read the name cache state of this
|
|
object and update it during minification so that it may be
|
|
reused or externally persisted by the user.
|
|
|
|
- `ie8` (default `false`) - set to `true` to support IE8.
|
|
|
|
- `keep_classnames` (default: `undefined`) - pass `true` to prevent discarding or mangling
|
|
of class names. Pass a regular expression to only keep class names matching that regex.
|
|
|
|
- `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling
|
|
of function names. Pass a regular expression to only keep class names matching that regex.
|
|
Useful for code relying on `Function.prototype.name`. If the top level minify option
|
|
`keep_classnames` is `undefined` it will be overridden with the value of the top level
|
|
minify option `keep_fnames`.
|
|
|
|
- `safari10` (default: `false`) - pass `true` to work around Safari 10/11 bugs in
|
|
loop scoping and `await`. See `safari10` options in [`mangle`](#mangle-options)
|
|
and [`output`](#output-options) for details.
|
|
|
|
## Minify options structure
|
|
|
|
```javascript
|
|
{
|
|
parse: {
|
|
// parse options
|
|
},
|
|
compress: {
|
|
// compress options
|
|
},
|
|
mangle: {
|
|
// mangle options
|
|
|
|
properties: {
|
|
// mangle property options
|
|
}
|
|
},
|
|
output: {
|
|
// output options
|
|
},
|
|
sourceMap: {
|
|
// source map options
|
|
},
|
|
ecma: 5, // specify one of: 5, 6, 7 or 8
|
|
keep_classnames: false,
|
|
keep_fnames: false,
|
|
ie8: false,
|
|
module: false,
|
|
nameCache: null, // or specify a name cache object
|
|
safari10: false,
|
|
toplevel: false,
|
|
warnings: false,
|
|
}
|
|
```
|
|
|
|
### Source map options
|
|
|
|
To generate a source map:
|
|
```javascript
|
|
var result = Terser.minify({"file1.js": "var a = function() {};"}, {
|
|
sourceMap: {
|
|
filename: "out.js",
|
|
url: "out.js.map"
|
|
}
|
|
});
|
|
console.log(result.code); // minified output
|
|
console.log(result.map); // source map
|
|
```
|
|
|
|
Note that the source map is not saved in a file, it's just returned in
|
|
`result.map`. The value passed for `sourceMap.url` is only used to set
|
|
`//# sourceMappingURL=out.js.map` in `result.code`. The value of
|
|
`filename` is only used to set `file` attribute (see [the spec][sm-spec])
|
|
in source map file.
|
|
|
|
You can set option `sourceMap.url` to be `"inline"` and source map will
|
|
be appended to code.
|
|
|
|
You can also specify sourceRoot property to be included in source map:
|
|
```javascript
|
|
var result = Terser.minify({"file1.js": "var a = function() {};"}, {
|
|
sourceMap: {
|
|
root: "http://example.com/src",
|
|
url: "out.js.map"
|
|
}
|
|
});
|
|
```
|
|
|
|
If you're compressing compiled JavaScript and have a source map for it, you
|
|
can use `sourceMap.content`:
|
|
```javascript
|
|
var result = Terser.minify({"compiled.js": "compiled code"}, {
|
|
sourceMap: {
|
|
content: "content from compiled.js.map",
|
|
url: "minified.js.map"
|
|
}
|
|
});
|
|
// same as before, it returns `code` and `map`
|
|
```
|
|
|
|
If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.url`.
|
|
|
|
## Parse options
|
|
|
|
- `bare_returns` (default `false`) -- support top level `return` statements
|
|
|
|
- `ecma` (default: `8`) -- specify one of `5`, `6`, `7` or `8`. Note: this setting
|
|
is not presently enforced except for ES8 optional trailing commas in function
|
|
parameter lists and calls with `ecma` `8`.
|
|
|
|
- `html5_comments` (default `true`)
|
|
|
|
- `shebang` (default `true`) -- support `#!command` as the first line
|
|
|
|
## Compress options
|
|
|
|
- `arrows` (default: `true`) -- Converts `()=>{return x}` to `()=>x`. Class
|
|
and object literal methods will also be converted to arrow expressions if
|
|
the resultant code is shorter: `m(){return x}` becomes `m:()=>x`.
|
|
|
|
- `arguments` (default: `false`) -- replace `arguments[index]` with function
|
|
parameter name whenever possible.
|
|
|
|
- `booleans` (default: `true`) -- various optimizations for boolean context,
|
|
for example `!!a ? b : c → a ? b : c`
|
|
|
|
- `booleans_as_integers` (default: `false`) -- Turn booleans into 0 and 1, also
|
|
makes comparisons with booleans use `==` and `!=` instead of `===` and `!==`.
|
|
|
|
- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables,
|
|
side effects permitting.
|
|
|
|
- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes,
|
|
e.g. `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary
|
|
nodes, e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
|
|
|
|
- `computed_props` (default: `true`) -- Transforms constant computed properties
|
|
into regular ones: `{["computed"]: 1}` is converted to `{computed: 1}`.
|
|
|
|
- `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional
|
|
expressions
|
|
|
|
- `dead_code` (default: `true`) -- remove unreachable code
|
|
|
|
- `defaults` (default: `true`) -- Pass `false` to disable most default
|
|
enabled `compress` transforms. Useful when you only want to enable a few
|
|
`compress` options while disabling the rest.
|
|
|
|
- `directives` (default: `true`) -- remove redundant or non-standard directives
|
|
|
|
- `drop_console` (default: `false`) -- Pass `true` to discard calls to
|
|
`console.*` functions. If you wish to drop a specific function call
|
|
such as `console.info` and/or retain side effects from function arguments
|
|
after dropping the function call then use `pure_funcs` instead.
|
|
|
|
- `drop_debugger` (default: `true`) -- remove `debugger;` statements
|
|
|
|
- `ecma` (default: `5`) -- Pass `6` or greater to enable `compress` options that
|
|
will transform ES5 code into smaller ES6+ equivalent forms.
|
|
|
|
- `evaluate` (default: `true`) -- attempt to evaluate constant expressions
|
|
|
|
- `expression` (default: `false`) -- Pass `true` to preserve completion values
|
|
from terminal statements without `return`, e.g. in bookmarklets.
|
|
|
|
- `global_defs` (default: `{}`) -- see [conditional compilation](#conditional-compilation)
|
|
|
|
- `hoist_funs` (default: `false`) -- hoist function declarations
|
|
|
|
- `hoist_props` (default: `true`) -- hoist properties from constant object and
|
|
array literals into regular variables subject to a set of constraints. For example:
|
|
`var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props`
|
|
works best with `mangle` enabled, the `compress` option `passes` set to `2` or higher,
|
|
and the `compress` option `toplevel` enabled.
|
|
|
|
- `hoist_vars` (default: `false`) -- hoist `var` declarations (this is `false`
|
|
by default because it seems to increase the size of the output in general)
|
|
|
|
- `if_return` (default: `true`) -- optimizations for if/return and if/continue
|
|
|
|
- `inline` (default: `true`) -- inline calls to function with simple/`return` statement:
|
|
- `false` -- same as `0`
|
|
- `0` -- disabled inlining
|
|
- `1` -- inline simple functions
|
|
- `2` -- inline functions with arguments
|
|
- `3` -- inline functions with arguments and variables
|
|
- `true` -- same as `3`
|
|
|
|
- `join_vars` (default: `true`) -- join consecutive `var` statements
|
|
|
|
- `keep_classnames` (default: `false`) -- Pass `true` to prevent the compressor from
|
|
discarding class names. Pass a regular expression to only keep class names matching
|
|
that regex. See also: the `keep_classnames` [mangle option](#mangle).
|
|
|
|
- `keep_fargs` (default: `true`) -- Prevents the compressor from discarding unused
|
|
function arguments. You need this for code which relies on `Function.length`.
|
|
|
|
- `keep_fnames` (default: `false`) -- Pass `true` to prevent the
|
|
compressor from discarding function names. Pass a regular expression to only keep
|
|
function names matching that regex. Useful for code relying on `Function.prototype.name`.
|
|
See also: the `keep_fnames` [mangle option](#mangle).
|
|
|
|
- `keep_infinity` (default: `false`) -- Pass `true` to prevent `Infinity` from
|
|
being compressed into `1/0`, which may cause performance issues on Chrome.
|
|
|
|
- `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops
|
|
when we can statically determine the condition.
|
|
|
|
- `module` (default `false`) -- Pass `true` when compressing an ES6 module. Strict
|
|
mode is implied and the `toplevel` option as well.
|
|
|
|
- `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions"
|
|
where the return value is discarded, to avoid the parens that the
|
|
code generator would insert.
|
|
|
|
- `passes` (default: `1`) -- The maximum number of times to run compress.
|
|
In some cases more than one pass leads to further compressed code. Keep in
|
|
mind more passes will take more time.
|
|
|
|
- `properties` (default: `true`) -- rewrite property access using the dot notation, for
|
|
example `foo["bar"] → foo.bar`
|
|
|
|
- `pure_funcs` (default: `null`) -- You can pass an array of names and
|
|
Terser will assume that those functions do not produce side
|
|
effects. DANGER: will not check if the name is redefined in scope.
|
|
An example case here, for instance `var q = Math.floor(a/b)`. If
|
|
variable `q` is not used elsewhere, Terser will drop it, but will
|
|
still keep the `Math.floor(a/b)`, not knowing what it does. You can
|
|
pass `pure_funcs: [ 'Math.floor' ]` to let it know that this
|
|
function won't produce any side effect, in which case the whole
|
|
statement would get discarded. The current implementation adds some
|
|
overhead (compression will be slower).
|
|
|
|
- `pure_getters` (default: `"strict"`) -- If you pass `true` for
|
|
this, Terser will assume that object property access
|
|
(e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects.
|
|
Specify `"strict"` to treat `foo.bar` as side-effect-free only when
|
|
`foo` is certain to not throw, i.e. not `null` or `undefined`.
|
|
|
|
- `reduce_funcs` (default: `true`) -- Allows single-use functions to be
|
|
inlined as function expressions when permissible allowing further
|
|
optimization. Enabled by default. Option depends on `reduce_vars`
|
|
being enabled. Some code runs faster in the Chrome V8 engine if this
|
|
option is disabled. Does not negatively impact other major browsers.
|
|
|
|
- `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and
|
|
used as constant values.
|
|
|
|
- `sequences` (default: `true`) -- join consecutive simple statements using the
|
|
comma operator. May be set to a positive integer to specify the maximum number
|
|
of consecutive comma sequences that will be generated. If this option is set to
|
|
`true` then the default `sequences` limit is `200`. Set option to `false` or `0`
|
|
to disable. The smallest `sequences` length is `2`. A `sequences` value of `1`
|
|
is grandfathered to be equivalent to `true` and as such means `200`. On rare
|
|
occasions the default sequences limit leads to very slow compress times in which
|
|
case a value of `20` or less is recommended.
|
|
|
|
- `side_effects` (default: `true`) -- Pass `false` to disable potentially dropping
|
|
functions marked as "pure". A function call is marked as "pure" if a comment
|
|
annotation `/*@__PURE__*/` or `/*#__PURE__*/` immediately precedes the call. For
|
|
example: `/*@__PURE__*/foo();`
|
|
|
|
- `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches
|
|
|
|
- `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or
|
|
variables (`"vars"`) in the top level scope (`false` by default, `true` to drop
|
|
both unreferenced functions and variables)
|
|
|
|
- `top_retain` (default: `null`) -- prevent specific toplevel functions and
|
|
variables from `unused` removal (can be array, comma-separated, RegExp or
|
|
function. Implies `toplevel`)
|
|
|
|
- `typeofs` (default: `true`) -- Transforms `typeof foo == "undefined"` into
|
|
`foo === void 0`. Note: recommend to set this value to `false` for IE10 and
|
|
earlier versions due to known issues.
|
|
|
|
- `unsafe` (default: `false`) -- apply "unsafe" transformations
|
|
([details](#the-unsafe-compress-option)).
|
|
|
|
- `unsafe_arrows` (default: `false`) -- Convert ES5 style anonymous function
|
|
expressions to arrow functions if the function body does not reference `this`.
|
|
Note: it is not always safe to perform this conversion if code relies on the
|
|
the function having a `prototype`, which arrow functions lack.
|
|
This transform requires that the `ecma` compress option is set to `6` or greater.
|
|
|
|
- `unsafe_comps` (default: `false`) -- Reverse `<` and `<=` to `>` and `>=` to
|
|
allow improved compression. This might be unsafe when an at least one of two
|
|
operands is an object with computed values due the use of methods like `get`,
|
|
or `valueOf`. This could cause change in execution order after operands in the
|
|
comparison are switching. Compression only works if both `comparisons` and
|
|
`unsafe_comps` are both set to true.
|
|
|
|
- `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)`
|
|
when both `args` and `code` are string literals.
|
|
|
|
- `unsafe_math` (default: `false`) -- optimize numerical expressions like
|
|
`2 * x * 3` into `6 * x`, which may give imprecise floating point results.
|
|
|
|
- `unsafe_methods` (default: false) -- Converts `{ m: function(){} }` to
|
|
`{ m(){} }`. `ecma` must be set to `6` or greater to enable this transform.
|
|
If `unsafe_methods` is a RegExp then key/value pairs with keys matching the
|
|
RegExp will be converted to concise methods.
|
|
Note: if enabled there is a risk of getting a "`<method name>` is not a
|
|
constructor" TypeError should any code try to `new` the former function.
|
|
|
|
- `unsafe_proto` (default: `false`) -- optimize expressions like
|
|
`Array.prototype.slice.call(a)` into `[].slice.call(a)`
|
|
|
|
- `unsafe_regexp` (default: `false`) -- enable substitutions of variables with
|
|
`RegExp` values the same way as if they are constants.
|
|
|
|
- `unsafe_undefined` (default: `false`) -- substitute `void 0` if there is a
|
|
variable named `undefined` in scope (variable name will be mangled, typically
|
|
reduced to a single character)
|
|
|
|
- `unused` (default: `true`) -- drop unreferenced functions and variables (simple
|
|
direct variable assignments do not count as references unless set to `"keep_assign"`)
|
|
|
|
- `warnings` (default: `false`) -- display warnings when dropping unreachable
|
|
code or unused declarations etc.
|
|
|
|
## Mangle options
|
|
|
|
- `eval` (default `false`) -- Pass `true` to mangle names visible in scopes
|
|
where `eval` or `with` are used.
|
|
|
|
- `keep_classnames` (default `false`) -- Pass `true` to not mangle class names.
|
|
Pass a regular expression to only keep class names matching that regex.
|
|
See also: the `keep_classnames` [compress option](#compress-options).
|
|
|
|
- `keep_fnames` (default `false`) -- Pass `true` to not mangle function names.
|
|
Pass a regular expression to only keep class names matching that regex.
|
|
Useful for code relying on `Function.prototype.name`. See also: the `keep_fnames`
|
|
[compress option](#compress-options).
|
|
|
|
- `module` (default `false`) -- Pass `true` an ES6 modules, where the toplevel
|
|
scope is not the global scope. Implies `toplevel`.
|
|
|
|
- `reserved` (default `[]`) -- Pass an array of identifiers that should be
|
|
excluded from mangling. Example: `["foo", "bar"]`.
|
|
|
|
- `toplevel` (default `false`) -- Pass `true` to mangle names declared in the
|
|
top level scope.
|
|
|
|
- `safari10` (default `false`) -- Pass `true` to work around the Safari 10 loop
|
|
iterator [bug](https://bugs.webkit.org/show_bug.cgi?id=171041)
|
|
"Cannot declare a let variable twice".
|
|
See also: the `safari10` [output option](#output-options).
|
|
|
|
Examples:
|
|
|
|
```javascript
|
|
// test.js
|
|
var globalVar;
|
|
function funcName(firstLongName, anotherLongName) {
|
|
var myVariable = firstLongName + anotherLongName;
|
|
}
|
|
```
|
|
```javascript
|
|
var code = fs.readFileSync("test.js", "utf8");
|
|
|
|
Terser.minify(code).code;
|
|
// 'function funcName(a,n){}var globalVar;'
|
|
|
|
Terser.minify(code, { mangle: { reserved: ['firstLongName'] } }).code;
|
|
// 'function funcName(firstLongName,a){}var globalVar;'
|
|
|
|
Terser.minify(code, { mangle: { toplevel: true } }).code;
|
|
// 'function n(n,a){}var a;'
|
|
```
|
|
|
|
### Mangle properties options
|
|
|
|
- `builtins` (default: `false`) — Use `true` to allow the mangling of builtin
|
|
DOM properties. Not recommended to override this setting.
|
|
|
|
- `debug` (default: `false`) — Mangle names with the original name still present.
|
|
Pass an empty string `""` to enable, or a non-empty string to set the debug suffix.
|
|
|
|
- `keep_quoted` (default: `false`) — Only mangle unquoted property names.
|
|
- `true` -- Quoted property names are automatically reserved and any unquoted
|
|
property names will not be mangled.
|
|
- `"strict"` -- Advanced, all unquoted property names are mangled unless
|
|
explicitly reserved.
|
|
|
|
- `regex` (default: `null`) — Pass a [RegExp literal or pattern string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) to only mangle property matching the regular expression.
|
|
|
|
- `reserved` (default: `[]`) — Do not mangle property names listed in the
|
|
`reserved` array.
|
|
|
|
## Output options
|
|
|
|
The code generator tries to output shortest code possible by default. In
|
|
case you want beautified output, pass `--beautify` (`-b`). Optionally you
|
|
can pass additional arguments that control the code output:
|
|
|
|
- `ascii_only` (default `false`) -- escape Unicode characters in strings and
|
|
regexps (affects directives with non-ascii characters becoming invalid)
|
|
|
|
- `beautify` (default `true`) -- whether to actually beautify the output.
|
|
Passing `-b` will set this to true, but you might need to pass `-b` even
|
|
when you want to generate minified code, in order to specify additional
|
|
arguments, so you can use `-b beautify=false` to override it.
|
|
|
|
- `braces` (default `false`) -- always insert braces in `if`, `for`,
|
|
`do`, `while` or `with` statements, even if their body is a single
|
|
statement.
|
|
|
|
- `comments` (default `false`) -- pass `true` or `"all"` to preserve all
|
|
comments, `"some"` to preserve some comments, a regular expression string
|
|
(e.g. `/^!/`) or a function.
|
|
|
|
- `ecma` (default `5`) -- set output printing mode. Set `ecma` to `6` or
|
|
greater to emit shorthand object properties - i.e.: `{a}` instead of `{a: a}`.
|
|
The `ecma` option will only change the output in direct control of the
|
|
beautifier. Non-compatible features in the abstract syntax tree will still
|
|
be output as is. For example: an `ecma` setting of `5` will **not** convert
|
|
ES6+ code to ES5.
|
|
|
|
- `indent_level` (default `4`)
|
|
|
|
- `indent_start` (default `0`) -- prefix all lines by that many spaces
|
|
|
|
- `inline_script` (default `true`) -- escape HTML comments and the slash in
|
|
occurrences of `</script>` in strings
|
|
|
|
- `keep_quoted_props` (default `false`) -- when turned on, prevents stripping
|
|
quotes from property names in object literals.
|
|
|
|
- `max_line_len` (default `false`) -- maximum line length (for minified code)
|
|
|
|
- `preamble` (default `null`) -- when passed it must be a string and
|
|
it will be prepended to the output literally. The source map will
|
|
adjust for this text. Can be used to insert a comment containing
|
|
licensing information, for example.
|
|
|
|
- `quote_keys` (default `false`) -- pass `true` to quote all keys in literal
|
|
objects
|
|
|
|
- `quote_style` (default `0`) -- preferred quote style for strings (affects
|
|
quoted property names and directives as well):
|
|
- `0` -- prefers double quotes, switches to single quotes when there are
|
|
more double quotes in the string itself. `0` is best for gzip size.
|
|
- `1` -- always use single quotes
|
|
- `2` -- always use double quotes
|
|
- `3` -- always use the original quotes
|
|
|
|
- `safari10` (default `false`) -- set this option to `true` to work around
|
|
the [Safari 10/11 await bug](https://bugs.webkit.org/show_bug.cgi?id=176685).
|
|
See also: the `safari10` [mangle option](#mangle-options).
|
|
|
|
- `semicolons` (default `true`) -- separate statements with semicolons. If
|
|
you pass `false` then whenever possible we will use a newline instead of a
|
|
semicolon, leading to more readable output of minified code (size before
|
|
gzip could be smaller; size after gzip insignificantly larger).
|
|
|
|
- `shebang` (default `true`) -- preserve shebang `#!` in preamble (bash scripts)
|
|
|
|
- `webkit` (default `false`) -- enable workarounds for WebKit bugs.
|
|
PhantomJS users should set this option to `true`.
|
|
|
|
- `wrap_iife` (default `false`) -- pass `true` to wrap immediately invoked
|
|
function expressions. See
|
|
[#640](https://github.com/mishoo/UglifyJS2/issues/640) for more details.
|
|
|
|
# Miscellaneous
|
|
|
|
### Keeping copyright notices or other comments
|
|
|
|
You can pass `--comments` to retain certain comments in the output. By
|
|
default it will keep JSDoc-style comments that contain "@preserve",
|
|
"@license" or "@cc_on" (conditional compilation for IE). You can pass
|
|
`--comments all` to keep all the comments, or a valid JavaScript regexp to
|
|
keep only comments that match this regexp. For example `--comments /^!/`
|
|
will keep comments like `/*! Copyright Notice */`.
|
|
|
|
Note, however, that there might be situations where comments are lost. For
|
|
example:
|
|
```javascript
|
|
function f() {
|
|
/** @preserve Foo Bar */
|
|
function g() {
|
|
// this function is never called
|
|
}
|
|
return something();
|
|
}
|
|
```
|
|
|
|
Even though it has "@preserve", the comment will be lost because the inner
|
|
function `g` (which is the AST node to which the comment is attached to) is
|
|
discarded by the compressor as not referenced.
|
|
|
|
The safest comments where to place copyright information (or other info that
|
|
needs to be kept in the output) are comments attached to toplevel nodes.
|
|
|
|
### The `unsafe` `compress` option
|
|
|
|
It enables some transformations that *might* break code logic in certain
|
|
contrived cases, but should be fine for most code. It assumes that standard
|
|
built-in ECMAScript functions and classes have not been altered or replaced.
|
|
You might want to try it on your own code; it should reduce the minified size.
|
|
Some examples of the optimizations made when this option is enabled:
|
|
|
|
- `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]`
|
|
- `new Object()` → `{}`
|
|
- `String(exp)` or `exp.toString()` → `"" + exp`
|
|
- `new Object/RegExp/Function/Error/Array (...)` → we discard the `new`
|
|
- `"foo bar".substr(4)` → `"bar"`
|
|
|
|
### Conditional compilation
|
|
|
|
You can use the `--define` (`-d`) switch in order to declare global
|
|
variables that Terser will assume to be constants (unless defined in
|
|
scope). For example if you pass `--define DEBUG=false` then, coupled with
|
|
dead code removal Terser will discard the following from the output:
|
|
```javascript
|
|
if (DEBUG) {
|
|
console.log("debug stuff");
|
|
}
|
|
```
|
|
|
|
You can specify nested constants in the form of `--define env.DEBUG=false`.
|
|
|
|
Terser will warn about the condition being always false and about dropping
|
|
unreachable code; for now there is no option to turn off only this specific
|
|
warning, you can pass `warnings=false` to turn off *all* warnings.
|
|
|
|
Another way of doing that is to declare your globals as constants in a
|
|
separate file and include it into the build. For example you can have a
|
|
`build/defines.js` file with the following:
|
|
```javascript
|
|
var DEBUG = false;
|
|
var PRODUCTION = true;
|
|
// etc.
|
|
```
|
|
|
|
and build your code like this:
|
|
|
|
terser build/defines.js js/foo.js js/bar.js... -c
|
|
|
|
Terser will notice the constants and, since they cannot be altered, it
|
|
will evaluate references to them to the value itself and drop unreachable
|
|
code as usual. The build will contain the `const` declarations if you use
|
|
them. If you are targeting < ES6 environments which does not support `const`,
|
|
using `var` with `reduce_vars` (enabled by default) should suffice.
|
|
|
|
### Conditional compilation API
|
|
|
|
You can also use conditional compilation via the programmatic API. With the difference that the
|
|
property name is `global_defs` and is a compressor property:
|
|
|
|
```javascript
|
|
var result = Terser.minify(fs.readFileSync("input.js", "utf8"), {
|
|
compress: {
|
|
dead_code: true,
|
|
global_defs: {
|
|
DEBUG: false
|
|
}
|
|
}
|
|
});
|
|
```
|
|
|
|
To replace an identifier with an arbitrary non-constant expression it is
|
|
necessary to prefix the `global_defs` key with `"@"` to instruct Terser
|
|
to parse the value as an expression:
|
|
```javascript
|
|
Terser.minify("alert('hello');", {
|
|
compress: {
|
|
global_defs: {
|
|
"@alert": "console.log"
|
|
}
|
|
}
|
|
}).code;
|
|
// returns: 'console.log("hello");'
|
|
```
|
|
|
|
Otherwise it would be replaced as string literal:
|
|
```javascript
|
|
Terser.minify("alert('hello');", {
|
|
compress: {
|
|
global_defs: {
|
|
"alert": "console.log"
|
|
}
|
|
}
|
|
}).code;
|
|
// returns: '"console.log"("hello");'
|
|
```
|
|
|
|
### Using native Terser AST with `minify()`
|
|
```javascript
|
|
// example: parse only, produce native Terser AST
|
|
|
|
var result = Terser.minify(code, {
|
|
parse: {},
|
|
compress: false,
|
|
mangle: false,
|
|
output: {
|
|
ast: true,
|
|
code: false // optional - faster if false
|
|
}
|
|
});
|
|
|
|
// result.ast contains native Terser AST
|
|
```
|
|
```javascript
|
|
// example: accept native Terser AST input and then compress and mangle
|
|
// to produce both code and native AST.
|
|
|
|
var result = Terser.minify(ast, {
|
|
compress: {},
|
|
mangle: {},
|
|
output: {
|
|
ast: true,
|
|
code: true // optional - faster if false
|
|
}
|
|
});
|
|
|
|
// result.ast contains native Terser AST
|
|
// result.code contains the minified code in string form.
|
|
```
|
|
|
|
### Working with Terser AST
|
|
|
|
Traversal and transformation of the native AST can be performed through
|
|
[`TreeWalker`](https://github.com/fabiosantoscode/terser/blob/master/lib/ast.js) and
|
|
[`TreeTransformer`](https://github.com/fabiosantoscode/terser/blob/master/lib/transform.js)
|
|
respectively.
|
|
|
|
Largely compatible native AST examples can be found in the original UglifyJS
|
|
documentation. See: [tree walker](http://lisperator.net/uglifyjs/walk) and
|
|
[tree transform](http://lisperator.net/uglifyjs/transform).
|
|
|
|
### ESTree / SpiderMonkey AST
|
|
|
|
Terser has its own abstract syntax tree format; for
|
|
[practical reasons](http://lisperator.net/blog/uglifyjs-why-not-switching-to-spidermonkey-ast/)
|
|
we can't easily change to using the SpiderMonkey AST internally. However,
|
|
Terser now has a converter which can import a SpiderMonkey AST.
|
|
|
|
For example [Acorn][acorn] is a super-fast parser that produces a
|
|
SpiderMonkey AST. It has a small CLI utility that parses one file and dumps
|
|
the AST in JSON on the standard output. To use Terser to mangle and
|
|
compress that:
|
|
|
|
acorn file.js | terser -p spidermonkey -m -c
|
|
|
|
The `-p spidermonkey` option tells Terser that all input files are not
|
|
JavaScript, but JS code described in SpiderMonkey AST in JSON. Therefore we
|
|
don't use our own parser in this case, but just transform that AST into our
|
|
internal AST.
|
|
|
|
### Use Acorn for parsing
|
|
|
|
More for fun, I added the `-p acorn` option which will use Acorn to do all
|
|
the parsing. If you pass this option, Terser will `require("acorn")`.
|
|
|
|
Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but
|
|
converting the SpiderMonkey tree that Acorn produces takes another 150ms so
|
|
in total it's a bit more than just using Terser's own parser.
|
|
|
|
[acorn]: https://github.com/ternjs/acorn
|
|
[sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k
|
|
|
|
### Terser Fast Minify Mode
|
|
|
|
It's not well known, but whitespace removal and symbol mangling accounts
|
|
for 95% of the size reduction in minified code for most JavaScript - not
|
|
elaborate code transforms. One can simply disable `compress` to speed up
|
|
Terser builds by 3 to 4 times.
|
|
|
|
| d3.js | size | gzip size | time (s) |
|
|
| --- | ---: | ---: | ---: |
|
|
| original | 451,131 | 108,733 | - |
|
|
| terser@3.7.5 mangle=false, compress=false | 316,600 | 85,245 | 0.82 |
|
|
| terser@3.7.5 mangle=true, compress=false | 220,216 | 72,730 | 1.45 |
|
|
| terser@3.7.5 mangle=true, compress=true | 212,046 | 70,954 | 5.87 |
|
|
| babili@0.1.4 | 210,713 | 72,140 | 12.64 |
|
|
| babel-minify@0.4.3 | 210,321 | 72,242 | 48.67 |
|
|
| babel-minify@0.5.0-alpha.01eac1c3 | 210,421 | 72,238 | 14.17 |
|
|
|
|
To enable fast minify mode from the CLI use:
|
|
```
|
|
terser file.js -m
|
|
```
|
|
To enable fast minify mode with the API use:
|
|
```js
|
|
Terser.minify(code, { compress: false, mangle: true });
|
|
```
|
|
|
|
#### Source maps and debugging
|
|
|
|
Various `compress` transforms that simplify, rearrange, inline and remove code
|
|
are known to have an adverse effect on debugging with source maps. This is
|
|
expected as code is optimized and mappings are often simply not possible as
|
|
some code no longer exists. For highest fidelity in source map debugging
|
|
disable the `compress` option and just use `mangle`.
|
|
|
|
### Compiler assumptions
|
|
|
|
To allow for better optimizations, the compiler makes various assumptions:
|
|
|
|
- `.toString()` and `.valueOf()` don't have side effects, and for built-in
|
|
objects they have not been overridden.
|
|
- `undefined`, `NaN` and `Infinity` have not been externally redefined.
|
|
- `arguments.callee`, `arguments.caller` and `Function.prototype.caller` are not used.
|
|
- The code doesn't expect the contents of `Function.prototype.toString()` or
|
|
`Error.prototype.stack` to be anything in particular.
|
|
- Getting and setting properties on a plain object does not cause other side effects
|
|
(using `.watch()` or `Proxy`).
|
|
- Object properties can be added, removed and modified (not prevented with
|
|
`Object.defineProperty()`, `Object.defineProperties()`, `Object.freeze()`,
|
|
`Object.preventExtensions()` or `Object.seal()`).
|
|
|
|
### Build Tools and Adaptors using Terser
|
|
|
|
https://www.npmjs.com/browse/depended/terser
|
|
|
|
### Replacing `uglify-es` with `terser` in a project using `yarn`
|
|
|
|
A number of JS bundlers and uglify wrappers are still using buggy versions
|
|
of `uglify-es` and have not yet upgraded to `terser`. If you are using `yarn`
|
|
you can add the following alias to your project's `package.json` file:
|
|
|
|
```js
|
|
"resolutions": {
|
|
"uglify-es": "npm:terser"
|
|
}
|
|
```
|
|
|
|
to use `terser` instead of `uglify-es` in all deeply nested dependencies
|
|
without changing any code.
|
|
|
|
Note: for this change to take effect you must run the following commands
|
|
to remove the existing `yarn` lock file and reinstall all packages:
|
|
|
|
```
|
|
$ rm -rf node_modules yarn.lock
|
|
$ yarn
|
|
```
|
|
|
|
# Reporting issues
|
|
|
|
In the terser CLI we use [source-map-support](https://npmjs.com/source-map-support) to produce good error stacks. In your own app, you're expected to enable source-map-support (read their docs) to have nice stack traces that will make good issues.
|
|
|
|
# README.md Patrons:
|
|
|
|
*note*: You can support this project on patreon: <a target="_blank" rel="nofollow" href="https://www.patreon.com/fabiosantoscode"><img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" alt="patron" width="100px" height="auto"></a>. Check out [PATRONS.md](https://github.com/terser-js/terser/blob/master/PATRONS.md) for our first-tier patrons.
|
|
|
|
These are the second-tier patrons. Great thanks for your support!
|
|
|
|
* CKEditor 
|
|
* 38elements 
|