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99 lines
3.3 KiB
99 lines
3.3 KiB
6 years ago
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# event-emitter
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## Environment agnostic event emitter
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### Installation
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$ npm install event-emitter
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To port it to Browser or any other (non CJS) environment, use your favorite CJS bundler. No favorite yet? Try: [Browserify](http://browserify.org/), [Webmake](https://github.com/medikoo/modules-webmake) or [Webpack](http://webpack.github.io/)
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### Usage
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```javascript
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var ee = require('event-emitter');
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var MyClass = function () { /* .. */ };
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ee(MyClass.prototype); // All instances of MyClass will expose event-emitter interface
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var emitter = new MyClass(), listener;
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emitter.on('test', listener = function (args) {
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// … react to 'test' event
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});
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emitter.once('test', function (args) {
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// … react to first 'test' event (invoked only once!)
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});
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emitter.emit('test', arg1, arg2/*…args*/); // Two above listeners invoked
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emitter.emit('test', arg1, arg2/*…args*/); // Only first listener invoked
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emitter.off('test', listener); // Removed first listener
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emitter.emit('test', arg1, arg2/*…args*/); // No listeners invoked
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```
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### Additional utilities
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#### allOff(obj) _(event-emitter/all-off)_
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Removes all listeners from given event emitter object
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#### hasListeners(obj[, name]) _(event-emitter/has-listeners)_
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Whether object has some listeners attached to the object.
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When `name` is provided, it checks listeners for specific event name
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```javascript
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var emitter = ee();
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var hasListeners = require('event-emitter/has-listeners');
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var listener = function () {};
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hasListeners(emitter); // false
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emitter.on('foo', listener);
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hasListeners(emitter); // true
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hasListeners(emitter, 'foo'); // true
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hasListeners(emitter, 'bar'); // false
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emitter.off('foo', listener);
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hasListeners(emitter, 'foo'); // false
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```
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#### pipe(source, target[, emitMethodName]) _(event-emitter/pipe)_
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Pipes all events from _source_ emitter onto _target_ emitter (all events from _source_ emitter will be emitted also on _target_ emitter, but not other way).
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Returns _pipe_ object which exposes `pipe.close` function. Invoke it to close configured _pipe_.
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It works internally by redefinition of `emit` method, if in your interface this method is referenced differently, provide its name (or symbol) with third argument.
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#### unify(emitter1, emitter2) _(event-emitter/unify)_
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Unifies event handling for two objects. Events emitted on _emitter1_ would be also emitted on _emitter2_, and other way back.
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Non reversible.
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```javascript
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var eeUnify = require('event-emitter/unify');
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var emitter1 = ee(), listener1, listener3;
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var emitter2 = ee(), listener2, listener4;
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emitter1.on('test', listener1 = function () { });
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emitter2.on('test', listener2 = function () { });
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emitter1.emit('test'); // Invoked listener1
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emitter2.emit('test'); // Invoked listener2
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var unify = eeUnify(emitter1, emitter2);
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emitter1.emit('test'); // Invoked listener1 and listener2
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emitter2.emit('test'); // Invoked listener1 and listener2
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emitter1.on('test', listener3 = function () { });
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emitter2.on('test', listener4 = function () { });
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emitter1.emit('test'); // Invoked listener1, listener2, listener3 and listener4
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emitter2.emit('test'); // Invoked listener1, listener2, listener3 and listener4
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```
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### Tests [](https://travis-ci.org/medikoo/event-emitter)
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$ npm test
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