forked from zhurui/management
71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
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# from2 [](https://flattr.com/submit/auto?user_id=hughskennedy&url=http://github.com/hughsk/from2&title=from2&description=hughsk/from2%20on%20GitHub&language=en_GB&tags=flattr,github,javascript&category=software)[](http://github.com/hughsk/stability-badges) #
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`from2` is a high-level module for creating readable streams that properly handle backpressure.
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Convience wrapper for
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[readable-stream](http://github.com/isaacs/readable-stream)'s `ReadableStream`
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base class, with an API lifted from
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[from](http://github.com/dominictarr/from) and
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[through2](http://github.com/rvagg/through2).
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## Usage ##
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[](https://nodei.co/npm/from2)
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### `stream = from2([opts], read)` ###
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Where `opts` are the options to pass on to the `ReadableStream` constructor,
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and `read(size, next)` is called when data is requested from the stream.
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* `size` is the recommended amount of data (in bytes) to retrieve.
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* `next(err)` should be called when you're ready to emit more data.
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For example, here's a readable stream that emits the contents of a given
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string:
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``` javascript
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var from = require('from2')
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function fromString(string) {
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return from(function(size, next) {
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// if there's no more content
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// left in the string, close the stream.
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if (string.length <= 0) return next(null, null)
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// Pull in a new chunk of text,
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// removing it from the string.
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var chunk = string.slice(0, size)
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string = string.slice(size)
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// Emit "chunk" from the stream.
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next(null, chunk)
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})
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}
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// pipe "hello world" out
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// to stdout.
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fromString('hello world').pipe(process.stdout)
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```
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### `stream = from2.obj([opts], read)` ###
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Shorthand for `from2({ objectMode: true }, read)`.
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### `createStream = from2.ctor([opts], read)` ###
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If you're creating similar streams in quick succession you can improve
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performance by generating a stream **constructor** that you can reuse instead
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of creating one-off streams on each call.
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Takes the same options as `from2`, instead returning a constructor which you
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can use to create new streams.
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### See Also
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- [from2-array](https://github.com/binocarlos/from2-array) - Create a from2 stream based on an array of source values.
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- [from2-string](https://github.com/yoshuawuyts/from2-string) - Create a stream from a string. Sugary wrapper around from2.
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## License ##
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MIT. See [LICENSE.md](http://github.com/hughsk/from2/blob/master/LICENSE.md) for details.
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