getType.html

<script type="text/javascript">
	function getType(x) {
		if (x == null) return "null";

		var t = typeof x;
		if (t != 'object') return t;

		var c = Object.prototype.toString.apply(x);
		c = c.substring(8, c.length - 1); 

		if (c != "Object") return c;

		if (x.constructor == Object) return c; 

		if ("classname" in x.constructor.prototype && 
			typeof x.constructor.prototype.classname == 'string') 
			return x.constructor.prototype.classname;

		return "<unknown type>";
	}

	var foo = function() {}

	var str= 'message';
	var num = 10;
	var obj = {};
	var arr = [];
	var n = null;
	var x;
	var _undefined = undefined;

	document.write(getType(num)); 					// 'number'
	document.write("<br>" + getType(str)); 			// 'string'
	document.write("<br>" + getType(obj)); 			// 'Object'
	document.write("<br>" + getType(arr)); 			// 'Array'
	document.write("<br>" + getType(foo)); 			// 'function'
	document.write("<br>" + getType(n)); 			// 'null'
	document.write("<br>" + getType(x)); 			// 'null'
	document.write("<br>" + getType(_undefined)); 	// 'null'
</script>