javascript - simplest way to use event emitter in ES6 - Stack Overflow

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This is my current implementation of an event emitter.

class Table {

  set onDiscard(cb) {
    this._onDiscard = cb;
  }

  notifyDiscard(s) {
    if (this._onDiscard) {
      this._onDiscard(s);
    }
  }
}

In the case of having multiple events this gets a burden.

What library/feature/implementation can I use so I can simplify this to a single line.

This is my current implementation of an event emitter.

class Table {

  set onDiscard(cb) {
    this._onDiscard = cb;
  }

  notifyDiscard(s) {
    if (this._onDiscard) {
      this._onDiscard(s);
    }
  }
}

In the case of having multiple events this gets a burden.

What library/feature/implementation can I use so I can simplify this to a single line.

• javascript
• events
• ember.js

Share Improve this question Follow edited May 2, 2015 at 17:06 user663031 asked May 2, 2015 at 15:07 eguneyseguneys 6,40677 gold badges3434 silver badges8181 bronze badges 2

• 1 The ecmascript6 tag is for questions specifically about ES6 features and behaviors . Don't use it if you are merely using ES6. – Felix Kling Commented May 2, 2015 at 15:45
• Why not just extend EventEmitter? – James Commented Dec 11, 2015 at 20:17

Add a ment  | 

4 Answers 4

Sorted by: Reset to default 5

Here's a simple one that supports multiple handlers:

class Table {
    on(type, cb) {
        this['_on' + type] = this['_on' + type] || [];
        this['_on' + type].push(cb);
    }

    emit(type, args) {
        this['_on' + type] && this['_on' + type].forEach((cb) => { cb(args) });
    }
}

var table = new Table();

table.on('started', function() { alert('started'); });
table.emit('started');

Why not make the event type a string?

class Table {
  on(eventType, cb) {
    this["_on" + eventType] = cb;
  }
  notify(eventType, s) {
    if(this["_on" + eventType]) {
      this["_on" + eventType](s);
    }
  }
}

Do you mean ES6 specifically or just ECMAScript? Since ES6 is backwards patible you could use any event library in ES5 (javascript) out there.

I'd suggest Backbone, as what you're doing seems to be model/view logic, which Backbone is actually very good at. It is very minimalistic, has it's own event emitter / listener (see Events section) implementation which is very similar to the one used by the DOM internally, and it helps separating your view and model logic very well.

I have implemented a simple app recently as a proof of concept using Backbone with ES6 and it's patible just the way you'd expect. Extending the base classes using ES6's extend does just what underscore's extend does when calling extend as suggested in Backbone's docs.

I used babeljs for transpilation in that case.

If you're using Ember, it has perfectly good mechanisms for emitters and notifiers. There's no reason not to use them. There's also no reason to use another, different class mechanism, just because it happens to exist in ES6, when Ember already provides one. Nor should you try to somehow awkwardly marry the Ember world with the ES6 class world.

Remember that ES6 classes (which some people say should not have been in the spec in the first place) are merely light syntactic sugar over JS prototype-based classes. So you should ask yourself the question: if I was already using Ember, would I implement my own emitter/notifier system using prototype-based classes? I doubt it. There's no reason to have two parallel class paradigms. Dance with the one you brought.

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