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    <p>When you assign the function to the click handler, a <a href="http://www.jibbering.com/faq/faq_notes/closures.html" rel="noreferrer">closure</a> is created.</p> <p>Basically a closure is formed when you nest functions, inner functions can refer to the variables present in their outer enclosing functions even after their parent functions have already executed.</p> <p>At the time that the click event is executed, the handler refers to the last value that the <code>i</code> variable had, because that variable is stored on the closure.</p> <p>As you noticed, by wrapping the click handler function in order to accept the <code>i</code> variable as an argument, and returning another function (basically create another closure) it works as you expect:</p> <pre><code>for ( var i = 0; i &lt; 4; i++ ) { var a = document.createElement( "a" ); a.onclick = (function(j) { // a closure is created return function () { alert(j); } }(i)); document.getElementById( "foo" ).appendChild( a ); } </code></pre> <p>When you iterate, actually create 4 functions, each function store a reference to <code>i</code> at the time it was created (by passing <code>i</code>), this value is stored on the outer closure and the inner function is executed when the click event fires.</p> <p>I use the following snippet to explain closures (and a very basic concept of <a href="http://en.wikipedia.org/wiki/Curry_(programming)" rel="noreferrer">curry</a>), I think that a simple example can make easier to get the concept:</p> <pre><code>// a function that generates functions to add two numbers function addGenerator (x) { // closure that stores the first number return function (y){ // make the addition return x + y; }; } var plusOne = addGenerator(1), // create two number adding functions addFive = addGenerator(5); alert(addFive(10)); // 15 alert(plusOne(10)); // 11 </code></pre>
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    1. COTaylor, I am happy for you, I'll let you finish, but this post is the best of all time, of all time.
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    3. COOne day, people will have forgotten about Kanye West, as I had, and all memes referring to him will just come off as rude and a little strange.
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