What is this JavaScript parameter syntax called?
<p>I've seen a few JavaScript code examples that use this sort of syntax:</p>

<pre><code>function(foo:String) {
  // code
}
</code></pre>

<p>I assume it does some sort of typecasting, but haven't been able to find much information about this syntax. Does anyone know what this is called, and where it is documented? Is this strict JavaScript or a browser extension?</p>
