forked from zhurui/management
52 lines
1012 B
Markdown
52 lines
1012 B
Markdown
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# once
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Only call a function once.
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## usage
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```javascript
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var once = require('once')
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function load (file, cb) {
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cb = once(cb)
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loader.load('file')
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loader.once('load', cb)
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loader.once('error', cb)
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}
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```
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Or add to the Function.prototype in a responsible way:
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```javascript
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// only has to be done once
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require('once').proto()
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function load (file, cb) {
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cb = cb.once()
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loader.load('file')
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loader.once('load', cb)
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loader.once('error', cb)
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}
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```
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Ironically, the prototype feature makes this module twice as
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complicated as necessary.
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To check whether you function has been called, use `fn.called`. Once the
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function is called for the first time the return value of the original
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function is saved in `fn.value` and subsequent calls will continue to
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return this value.
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```javascript
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var once = require('once')
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function load (cb) {
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cb = once(cb)
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var stream = createStream()
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stream.once('data', cb)
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stream.once('end', function () {
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if (!cb.called) cb(new Error('not found'))
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})
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}
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```
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