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    <p>First I want to correct Greg: <code>function abc(){}</code> is scoped too &mdash; the name <code>abc</code> is defined in the scope where this definition is encountered. Example:</p> <pre><code>function xyz(){ function abc(){}; // abc is defined here... } // ...but not here </code></pre> <p>Secondly, it is possible to combine both styles:</p> <pre><code>var xyz = function abc(){}; </code></pre> <p><code>xyz</code> is going to be defined as usual, <code>abc</code> is undefined in all browsers but Internet&nbsp;Explorer &mdash; do not rely on it being defined. But it will be defined inside its body:</p> <pre><code>var xyz = function abc(){ // xyz is visible here // abc is visible here } // xyz is visible here // abc is undefined here </code></pre> <p>If you want to alias functions on all browsers, use this kind of declaration:</p> <pre><code>function abc(){}; var xyz = abc; </code></pre> <p>In this case, both <code>xyz</code> and <code>abc</code> are aliases of the same object:</p> <pre><code>console.log(xyz === abc); // prints "true" </code></pre> <p>One compelling reason to use the combined style is the "name" attribute of function objects (<strong>not supported by Internet&nbsp;Explorer</strong>). Basically when you define a function like</p> <pre><code>function abc(){}; console.log(abc.name); // prints "abc" </code></pre> <p>its name is automatically assigned. But when you define it like</p> <pre><code>var abc = function(){}; console.log(abc.name); // prints "" </code></pre> <p>its name is empty &mdash; we created an anonymous function and assigned it to some variable.</p> <p>Another good reason to use the combined style is to use a short internal name to refer to itself, while providing a long non-conflicting name for external users:</p> <pre><code>// Assume really.long.external.scoped is {} really.long.external.scoped.name = function shortcut(n){ // Let it call itself recursively: shortcut(n - 1); // ... // Let it pass itself as a callback: someFunction(shortcut); // ... } </code></pre> <p>In the example above we can do the same with an external name, but it'll be too unwieldy (and slower).</p> <p><em>(Another way to refer to itself is to use <code>arguments.callee</code>, which is still relatively long, and not supported in the strict mode.)</em></p> <p>Deep down, JavaScript treats both statements differently. This is a function declaration:</p> <pre><code>function abc(){} </code></pre> <p><code>abc</code> here is defined everywhere in the current scope:</p> <pre><code>// We can call it here abc(); // Works // Yet, it is defined down there. function abc(){} // We can call it again abc(); // Works </code></pre> <p>Also, it hoisted through a <code>return</code> statement:</p> <pre><code>// We can call it here abc(); // Works return; function abc(){} </code></pre> <p>This is a function expression:</p> <pre><code>var xyz = function(){}; </code></pre> <p><code>xyz</code> here is defined from the point of assignment:</p> <pre><code>// We can't call it here xyz(); // UNDEFINED!!! // Now it is defined xyz = function(){} // We can call it here xyz(); // works </code></pre> <p>Function declaration vs. function expression is the real reason why there is a difference demonstrated by Greg.</p> <p>Fun fact:</p> <pre><code>var xyz = function abc(){}; console.log(xyz.name); // Prints "abc" </code></pre> <p>Personally, I prefer the "function expression" declaration because this way I can control the visibility. When I define the function like</p> <pre><code>var abc = function(){}; </code></pre> <p>I know that I defined the function locally. When I define the function like</p> <pre><code>abc = function(){}; </code></pre> <p>I know that I defined it globally providing that I didn't define <code>abc</code> anywhere in the chain of scopes. This style of definition is resilient even when used inside <code>eval()</code>. While the definition</p> <pre><code>function abc(){}; </code></pre> <p>depends on the context and may leave you guessing where it is actually defined, especially in the case of <code>eval()</code> &mdash; the answer is: It depends on the browser.</p>
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    1. POvar functionName = function() {} vs function functionName() {}
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    1. COI refer to RoBorg but he is nowhere to be found. Simple: RoBorg === Greg. That's how history can be rewritten in the age of internet. ;-)
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    2. COvar xyz = function abc(){}; console.log(xyz === abc); All browsers I've tested (Safari 4, Firefox 3.5.5, Opera 10.10) gives me "Undefined variable: abc".
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    3. COOverall I think this post does a good job of explaining the differences and the advantages of utilizing the function declaration. I'll agree to disagree as far as the benefits of utilizing function expression assignments to a variable especially since the "benefit" seems to be an advocation of declaring a global entity... and everyone knows that you shouldn't clutter the global namespace, right? ;-)
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