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copied!<p>The way I usually explain this to people is to show how it's similar to other JavaScript patterns.</p> <p>First, you should know that there are two ways to declare a function (actually, there's at least five, but these are the two main culprits):</p> <p><code>function foo() {/*code*/}</code></p> <p>and</p> <p><code>var foo = function() {/*code*/};</code></p> <p>Even if this construction looks strange, you probably use it all the time when attaching events:</p> <p><code>window.onload=function(){/*code*/};</code></p> <p>You should notice that the second form is not much different from a regular variable declaration:</p> <pre><code>var bar = 5; var baz = 'some string'; var foo = function() {/*code*/}; </code></pre> <p>But in JavaScript, you always have the choice between using a value directly or through a variable. If <code>bar</code> is <code>5</code>, then the next two statements are equivalent:</p> <pre><code>var myVal = bar * 100; // use 'bar' var myVal = 5 * 100; // don't use 'bar' </code></pre> <p>Well, if you can use <code>5</code> on its own, why can't you use <code>function() {\*code*\}</code> on its own too? In fact, you can. And that's called an anonymous function. So these two examples are equivalent as well:</p> <pre><code>var foo = function() {/*code*/}; // use 'foo' foo(); (function(){/*code*/}()); // don't use 'foo' </code></pre> <p>The only difference you should see is in the extra brackets. That's simply because if you start a line with the keyword <code>function</code>, the parser will think you are declaring a function using the very first pattern at the top of this answer and throw a syntax error exception. So wrap your entire anonymous function inside a pair of braces and the problem goes away. </p> <p>In other words, the following three statements are valid:</p> <pre><code>5; // pointless and stupid 'some string'; // pointless and stupid (function(){/*code*/}()); // wonderfully powerful </code></pre>

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