StackOverflow2013

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copied!<p>I could not care less about your system being callback, event or lambda-calculus based. For the bit you expose here, it seems rather well-written and promises to do a good job (although I'm curious about how you handled <code>removeEvent()</code> ;)).</p> <p>However, I have a few remarks about your implementation:</p> <ul> <li>it is unnecessary to check on which browser you execute each time you add an event handler.</li> </ul> <p>I am amazed at the number of people accepting the practice of checking existence of properties each time they are about to call them. Noone will swap your IE for a FF in the middle of a function call (and anyone stupid enough to define a <code>document.addEventListener</code> property other than an actual ECMA-5 replacement deserves to be flogged to death, if you ask me), so check which platform you're on at start and be done with it, like so:</p> <pre><code>if (doc.addEventListener) { addEvent = // ... freeEvent = // ... } else if (doc.attachEvent) { addEvent = // ... freeEvent = // ... } /* etc. */ </code></pre> <ul> <li>you offer an unified interface to attach a handler but, depending on the browser your code will execute on, the actual handler will behave differently.</li> </ul> <p>In IE8-, for instance, the target of the event will not be available the same way as in ECMA-5 conventions.</p> <p>If you want to offer a real cross-browser interface, you should provide an unified execution context to the event handlers. This could include a "cancel" function that would translate to something like:</p> <pre><code>cancel = function (e) { e.returnValue = false; }; // IE8- cancel = function (e) { e.preventDefault(); }; // ECMA-5 </code></pre> <p>you should also restore <code>this</code> to the target object under IE8-, and unify the <code>target</code> and <code>event.target</code> semantics.</p> <p>If you really want to be nice to programmers, you could also tackle a few oddities, like</p> <ul> <li>the load event not firing in IE8- when an image is already cached</li> <li>the absurdly complicated mouse wheel report system</li> </ul> <p>and probably a few others.</p> <p>The way I did it for my own purposes was to have a wrapper generated around the actual handler, that could take care of all the platform pecularities and establish a consistent execution context before calling the actual user code.</p> <p>A last remark: except for the beauty of it, I am not quite sure it is still necessary to support Netscape4-style events. But that is a matter of faith, so...</p>

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