Luiz Costa
ac4f232e5e
This change modifies the build scripts to use --legacy-peer-deps flag when installing npm dependencies to resolve potential peer dependency conflicts during the build process. The change is applied to both bash (build.sh) and batch (build.bat) build scripts.
80 lines
1.7 KiB
Markdown
80 lines
1.7 KiB
Markdown
# 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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## `once.strict(func)`
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Throw an error if the function is called twice.
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Some functions are expected to be called only once. Using `once` for them would
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potentially hide logical errors.
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In the example below, the `greet` function has to call the callback only once:
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```javascript
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function greet (name, cb) {
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// return is missing from the if statement
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// when no name is passed, the callback is called twice
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if (!name) cb('Hello anonymous')
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cb('Hello ' + name)
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}
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function log (msg) {
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console.log(msg)
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}
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// this will print 'Hello anonymous' but the logical error will be missed
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greet(null, once(msg))
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// once.strict will print 'Hello anonymous' and throw an error when the callback will be called the second time
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greet(null, once.strict(msg))
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```
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