ECMAScript defines 12 different [[Class]] values - see [section 8.6.2](http://ecma-international.org/ecma-262/5.1/#sec-8.6.2). However, $.type() only "recognizes" 8 of those 12 values. The 4 that it doesn't recognize are:

• "Arguments"
• "Error"
• "Math"
• "JSON"

I understand why jQuery ignores Math, JSON, or the arguments object - their "type" can easily be comprehended based on their name.

What I don't understand is why $.type refuses to recognize Error objects.

$.type( new Error ) // "object", but should be "error"

Error objects are one of the native ECMAScript types of objects. $.type should be able to recognize them. To enable this recognition, all you have to do is add "Error" to the space-separated list here:

// Populate the class2type map
jQuery.each("Boolean Number String Function Array Date RegExp Object".split(" "), function(i, name) {
    class2type[ "[object " + name + "]" ] = name.toLowerCase();
});

Like so:

// Populate the class2type map
jQuery.each("Boolean Number String Function Array Date RegExp Object Error".split(" "), function(i, name) {
    class2type[ "[object " + name + "]" ] = name.toLowerCase();
});

The [[Class]] value of all instances of any of the native Error constructors (e.g. Error, SyntaxError, etc.) is "Error", so that this small change in the jQuery source code should make $.type recognize all native Error objects.

Btw, I have created a corresponding thread on Stack Oveflow - see here: http://stackoverflow.com/q/11797707/425275.