Observer

A simple implementation of the Observer pattern with test coverage.

Works in browser and node environments, supports AMD module definition and RequireJS (The Observer object is therefore exposed as a module).

This module was created for my own usage but I decided to share it.

Why yet another implementation

There is already plenty of implementations of such a module such as the good EventEmitter. The reasons why I decided to do my own :

• lightweight
• can make every object observable
• the other implementations are not cross-environment (browser and node, install through npm or bower)
• most use subscribe/publish paradigm, this implementation uses named events which reduce boilerplate code
• ready to use with requirejs
• fast
• test coverage

Installation

With npm :

npm install quest-observer

With bower :

bower install quest-observer

Usage

You can make every object observable by using Observer.make :

// we can also use new function () {}
var o = {};
 
// you can now listen for events on object o !
Observable.make(o);
 
// this will print "world!"
o.on("hello", function () {
  console.log("world!");
});
 
// this will not be called
o.on("bonjour", function () {
  console.log("le monde!");
});
 
// emit and event
o.emit("hello");

Event handlers can stack :

var count = 0;
 
// generic handler
function increment() {
    count++;
}
 
// oups I used Ctrl+V 3 times!
obj.on("increment", increment);
obj.on("increment", increment);
obj.on("increment", increment);
 
obj.emit("increment");
 
// prints "3"
console.log(count);

emit also support parameters :

obj.on("message", function (name, age, data) {
    // prints "Jack (20): hello world!"
    console.log(name + "(" + age + ") : " + data.message);
});
 
obj.emit("message", "Jack", 20, {
    message: "hello world!"
});

You can clear your event listeners with clear :

var ptr = obj.on("event", callback);
 
// clear by using the event name and listener reference
obj.clear("event", callback);
 
// clear using the dispose handler returned by on()
ptr.dispose();

You can also listen for an event only once:

obj.once("complete", function () {
    // this will be called once regardless of number of "complete" events
});
 
obj.emit("complete");
obj.emit("complete");

License

Copyright (c) 2015, Pierre BEAUJEU

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.