EventEmitter.js

/*!
 * EventEmitter v0.1
 * https://github.com/JamesMGreene/phantomjs-extensions/
 *
 * Copyright © 2012: James Greene (Team Gunmetal, Inc.)
 * Released under the MIT license.
 * http://www.opensource.org/licenses/mit-license.php
 */

/*global exports:true, module:false */
/*jshint forin:true, noarg:true, noempty:true, eqeqeq:true, bitwise:true, strict:true, undef:true, unused:true, curly:true, browser:true, devel:true, es5:true, indent:4, maxerr:50 */ 
 
// Assumes this is being imported via `CJSRequire`
(function(window) {
    "use strict";

    /**
    * A basic event emitter.
    * Public API primarily taken from TJ Holowaychuk's https://github.com/component/emitter
    */
    var EventEmitter = function() {
        this._eventMap = {};
    };
    
    var contextualize = function(callback) {
        var cbContext;
        if (typeof callback === "function") {
            cbContext = {
                "callback": callback
            };
        }
        else if (typeof callback === "object" && callback !== null) {
            cbContext = callback;
        }
        else {
            return null;
        }
        
        if (typeof cbContext.callback !== "function") {
            throw new TypeError("`callback` must either be a function or a contextual object");
        }
        
        if (!cbContext.hasOwnProperty("wrappedCallback")) {
            cbContext.wrappedCallback = null;
        }
        if (!cbContext.hasOwnProperty("binding")) {
            cbContext.binding = null;
        }
        if (!cbContext.hasOwnProperty("onlyOnce") || typeof cbContext.onlyOnce !== "boolean") {
            cbContext.onlyOnce = false;
        }
        
        return cbContext;
    };

    Object.defineProperties(EventEmitter.prototype, {
        "on": {
            value: function(eventType, callback, runFirst) {
                var cbContext = contextualize(callback),
                    op = !!runFirst ? "unshift" : "push";
                (this._eventMap[eventType] = this._eventMap[eventType] || [])[op](cbContext);
                
                // Chain!
                return this;
            }
        },

        "off": {
            value: function(eventType, callback) {
                var cbContexts = this._eventMap[eventType];
                if (cbContexts) {
                    // Remove all handlers for this `eventType`
                    if (typeof callback === "undefined") {
                        delete this._eventMap[eventType];
                    }
                    // Remove any handlers for this `eventType` that match the provided `callback`
                    else {
                        var cbContextToRemove = contextualize(callback);
                        for (var i = 0; i < cbContexts.length; i++) {
                            if (cbContexts[i].callback === cbContextToRemove.callback) {
                                cbContexts.splice(i--, 1);
                            }
                        }
                    }
                }
                // Chain!
                return this;
            }
        },

        "once": {
            value: function(eventType, callback, runFirst) {
                var cbContext = contextualize(callback);
                cbContext.onlyOnce = true;
                
                return this.on(eventType, cbContext, runFirst);
            }
        },

        "emit": {
            value: function(eventType) {
                var args = [].slice.call(arguments, 1),
                    readonlyCallbacks = this.listeners(eventType);
                for (var i = 0, len = readonlyCallbacks.length; i < len; i++) {
                    var cbContext = readonlyCallbacks[i];
                    if (cbContext.onlyOnce) {
                        this.off(eventType, cbContext);
                    }
                    (cbContext.wrappedCallback || cbContext.callback).apply(cbContext.binding, args);
                }
                // Chain!
                return this;
            }
        },

        "listeners": {
            value: function(eventType) {
                // Return a COPY of the handlers array for `eventType`, or an empty array if no callbacks have been added
                var callbacks = this._eventMap[eventType];
                return (callbacks && callbacks.length ? callbacks.slice(0) : []);
            }
        },

        "hasListeners": {
            value: function(eventType) {
                var callbacks = this._eventMap[eventType];
                return callbacks && callbacks.length;
            }
        }
    });

    return exports = (module || {}).exports = EventEmitter;

})(this);