ampersand-events

Part of the Ampersand.js toolkit for building clientside applications.

A module that can be mixed into any object to make it able to trigger events and be listened to. This is heavily based on Backbone Events with a few modifications.

Install

npm install ampersand-events

Example usage

ampersand-events is simply an object of methods. So you can easily add those to any object using any of the following techniques.

Adding events to a constructor or "class"

var Events = require('ampersand-events');
var assign = require('lodash.assign');
 
// Create some constructor
var MyConstructor = function () {};
 
// Extend the prototype with the event methods and your own:
assign(MyConstructor.prototype, Events, {
    myOtherMethods: function () {}
});
 
// Now we can trigger and listen for events on
// any instances created with our constructor.
var myObj = new MyConstructor();

Using with plain objects

var Events = require('ampersand-events');
 
// Events has an `createEmitter` helper that you can pass
// any object to to add event methods to.
var myObj = {};
Events.createEmitter(myObj);
 
// it now has event methods
myObj.trigger('some event');

Using as an event bus / or pubsub channel

You can call Event.createEmitter() without any arguments to create an "empty" event emitter.

This can be really useful for creating what you might call an "event bus" or "pubsub" mechanism for things like application events, or whatnot.

Say you created a module like this:

var Events = require('ampersand-events');

module.exports = Events.createEmitter();

Any module in your app could now require this module and trigger events that other modules in your app could listen for.

API Reference

createEmitter Events.createEmitter([object])

Modifies any passed object to add event capabilities to it. If you don't pass any object, it simply creates and returns a new object with event capabilities.

• object {Object} [Optional] Any object you want to add event capabilities to.

It simply adds the event methods to the passed in object.

var myObj = {};
Events.createEmitter(myObj);
 
myObj.on('customEvent', function () {
    // handle event
});
myObj.trigger('customEvent');

on eventObj.on(eventName, callback, [context])

(aliased as bind for backwards compatibility)

Bind a function to be called each time the eventName is triggered on that object.

• eventName {String} The name of the event to listen for. Can also be "all" which will call your callback no matter what event is triggered.
• callback {Function} The function to call when the event is triggered.
• context {Object}[optional] If you provide an object here it will be the value of this inside your callback function.

myObj.on('anything', function () {
    console.log('I can handle anything!');
});

once eventObj.once(eventName, callback, [context])

Exactly like on but removes itself after getting called once no matter how many times the event is triggered.

off eventObj.off([eventName], [callback], [context])

(aliased as unbind for backwards compatibility)

Remove previously bound callback(s) from the object. If no context is specified all versions of callback no matter what context was given will be removed. If no callback was specified, all callbacks for that given eventName will be removed. If no eventName was specified callbacks for all events are removed.

• eventName {String} The name of the event to remove. Pass null to "leave blank".
• callback {Function} The function to remove or pass null to "leave blank".
• context {Object} Remove all callbacks with this context.

These can be used in any combination as shown below:

// Removes the `onChange` callback
eventObj.off('change', onChange);
 
// Removes all callbacks listening for 'change' events
eventObj.off('change');
 
// Removes the `onChange` callback for any event
eventObj.off(null, onChange);
 
// Removes all callbacks for a given `context`
eventObj.off(null, null, context);
 
// Removes all callbacks no matter what
eventObj.off();

trigger eventObj.trigger(eventName, [argsToPassOn])

Triggers all the callbacks for the given eventName.

• eventName {String} Name of event, or space-delimited list of events.
• argsToPassOn { ... } Any additional arguments will simply be used to call the callbacks that are listening for this event.

eventObj.on('change', function (payload) {
    // `payload` will be the `{some: 'object'}` instance
    // from below.
});
eventObj.trigger('change', {some: 'object'});

listenTo eventObj.listenTo(otherEventObj, eventName, callback)

Tell an eventObject to listen to eventName on another object. This is another form of on that makes it easier to create an object that listens to events from other objects and keep track of them. This makes it so we can easily listen to several different events from several different objects but make it simple to remove them all at once.

For example, if we use .listenTo to listen to model changes it cares about in an ampersand-view the view will know what callbacks it needs to unregister if it gets removed.

• otherEventObj {Event object} The other object to listen to.
• eventName {String} Event to listen to (can also be space delimited list of events).
• callback {Function} The function to call when event occurs.

Note: the callback will always be called with the eventObj as the this value.

view.listenTo(model, 'change', view.render);
// when `view.render` is called `this` will be `view`

listenToOnce eventObj.listenToOnce(otherEventObj, eventName, callback)

Same as listenTo but it unregisters itself after getting called once no matter how many times the events is triggered.

listenToAndRun eventObj.listenToAndRun(otherEventObj, eventName, callback)

Same as listenTo but also immediately executes the registered callback once right away. This can be useful for things like methods that re-calculate totals, but that also need to be run once to calculate the initial value.

stopListening eventObj.stopListening([otherEventObj], [eventName], [callback])

Tells the eventObj to stop listening to events. Most commonly it's used without arguments to remove all callbacks an object registered before destroying the object. For example ampersand-view calls this.stopListening() as part of .remove().

However, you can also use stopListening with specific objects, events or callbacks.

• otherEventObj {Event object} The other object being listened to.
• eventName {String} A specific string or space-delimited list of events to stop listening to.
• callback {Function} A specific callback to remove.

These can be used in any combination as shown below:

// Stops listening to everything
eventObj.stopListening();
 
// Stop listening to a specific object
eventObj.stopListening(object);
 
// Stop listening to all 'change' events from any model
eventObj.stopListening(null, 'change');
 
// Remove just a specific `callback`
eventObj.stopListening(null, null, callback);

changelog

• 2.0.0 - switch to lodash v4

license

MIT