EventDispatcher.js

/**
 * EventDispatcher
 * @see http://www.fladdict.net/blog-jp/archives/2005/06/javascript.php
 * @see http://nanto.asablo.jp/blog/2007/03/23/1339498
 */
function EventDispatcher(thisObj) {
    if (this instanceof EventDispatcher) {
        this.addEventListener = addEventListener;
        this.removeEventListener = removeEventListener;
        this.dispatchEvent = dispatchEvent;
    }
    if (thisObj) {
        thisObj.addEventListener = addEventListener;
        thisObj.removeEventListener = removeEventListener;
        thisObj.dispatchEvent = dispatchEvent;
    }
    var ec = {};
    function addEventListener(type, listener) {
        if (typeof listener != 'function') return;
        if (ec[type] == null) { ec[type] = [listener]; return; }
        var listeners = ec[type];
        for (var i = 0, len = listeners.length; i < len; i++) {
            if (listeners[i] === listener) { return; }
        }
        listeners.push(listener);
    }
    function removeEventListener(type, listener) {
        if (ec[type] == null) return;
        var listeners = ec[type];
        for (var i = 0, len = listeners.length; i < len; i++) {
            if (listeners[i] === listener) { listeners.splice(i, 1); break; }
        }
    }
    function dispatchEvent(event) {
        if (ec[event.type] == null) return true;
        event.target = this;
        event.currentTarget = this;
        event.eventPhase = 2; // support target phase only.
        var canceled = false;
        event.preventDefault = function preventDefault() { if (event.cancelable) canceled = true; };
        event.stopPropagation = function stopPropagation() {};
        var listeners = ec[event.type];
        for (var i = 0, len = listeners.length; i < len; i++) {
            var res = listeners[i].call(event.currentTarget, event);
            if (event.cancelable && !canceled) {
                if (res == false || event.returnValue == false) canceled = true;
            }
        }
        return !canceled;
    }
}