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POWhat is difference between a callback-based and an event-based event handling system?
 

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  1. POWhat is difference between a callback-based and an event-based event handling system?
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    <p>I was working on a cross-browser event handling system. And I asked some developers to review my code. One of the developers said that my implementation is based on callbacks and not real events. What is the difference?</p> <p>I have provided the source code of my implementation below for your convenience (and also <a href="https://gist.github.com/erikroyall/6618740/" rel="nofollow noreferrer">as a gist</a>). So far, I haven't found any problems with it. It works fine with all browsers that I tested with.</p> <p>I'm sorry for the bad description of the problem, I am not familiar with that pure-event part.</p> <pre><code>var evento = (function (window) { var win = window , doc = win.document , _handlers = {} , addEvent , removeEvent , triggerEvent; addEvent = (function () { if (typeof doc.addEventListener === "function") { return function (el, evt, fn) { el.addEventListener(evt, fn, false); _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt].push(fn); }; } else if (typeof doc.attachEvent === "function") { return function (el, evt, fn) { el.attachEvent(evt, fn); _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt].push(fn); }; } else { return function (el, evt, fn) { el["on" + evt] = fn; _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt].push(fn); }; } }()); // removeEvent removeEvent = (function () { if (typeof doc.removeEventListener === "function") { return function (el, evt, fn) { el.removeEventListener(evt, fn, false); Helio.each(_handlers[el][evt], function (fun) { if (fun === fn) { _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt][_handlers[el][evt].indexOf(fun)] = undefined; } }); }; } else if (typeof doc.detachEvent === "function") { return function (el, evt, fn) { el.detachEvent(evt, fn); Helio.each(_handlers[el][evt], function (fun) { if (fun === fn) { _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt][_handlers[el][evt].indexOf(fun)] = undefined; } }); }; } else { return function (el, evt, fn) { el["on" + evt] = undefined; Helio.each(_handlers[el][evt], function (fun) { if (fun === fn) { _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; _handlers[el][evt][_handlers[el][evt].indexOf(fun)] = undefined; } }); }; } }()); // triggerEvent triggerEvent = function (el, evt) { _handlers[el] = _handlers[el] || {}; _handlers[el][evt] = _handlers[el][evt] || []; for (var _i = 0, _l = _handlers[el][evt].length; _i &lt; _l; _i += 1) { _handlers[el][evt][_i](); } }; return { add: addEvent, remove: removeEvent, trigger: triggerEvent, _handlers: _handlers }; }(this)); </code></pre>
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    1. COI don't know what that developer is getting at. Did you ask? An event system can be any system that responds to a particular action, and causes some behavior when that action takes place. A callback is just a function that can be passed to another function to be invoked at a later time.
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    2. CONote that in IE `typeof doc.attachEvent` returns `object` (where implemented) so those forks of your code will never be executed. Some host objects return `unknown`. Host objects are not required to conform to all details of ECMA-262, so you should not rely on them doing so.
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      1. POWhat is difference between a callback-based and an event-based event handling system?
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    3. COWhat he said was "Nice code. Only problem? You are using callbacks and not events. :) http://dean.edwards.name/weblog/2009/03/callbacks-vs-events/"
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