$X

dollarX.js

// extend version of $X
// $X(exp);
// $X(exp, context);
// $X(exp, type);
// $X(exp, context, type);
function $X (exp, context, type /* want type */) {
	if (typeof context == "function") {
		type    = context;
		context = null;
	}
	if (!context) context = document;
	exp = (context.ownerDocument || context).createExpression(exp, function (prefix) {
		var o = document.createNSResolver(context)(prefix);
		if (o) return o;
		return (document.contentType == "application/xhtml+xml") ? "http://www.w3.org/1999/xhtml" : "";
	});

	switch (type) {
		case String:  return exp.evaluate(context, XPathResult.STRING_TYPE, null).stringValue;
		case Number:  return exp.evaluate(context, XPathResult.NUMBER_TYPE, null).numberValue;
		case Boolean: return exp.evaluate(context, XPathResult.BOOLEAN_TYPE, null).booleanValue;
		case Array:
			var result = exp.evaluate(context, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
			for (var ret = [], i = 0, len = result.snapshotLength; i < len; i++) {
				ret.push(result.snapshotItem(i));
			}
			return ret;
		case undefined:
			var result = exp.evaluate(context, XPathResult.ANY_TYPE, null);
			switch (result.resultType) {
				case XPathResult.STRING_TYPE : return result.stringValue;
				case XPathResult.NUMBER_TYPE : return result.numberValue;
				case XPathResult.BOOLEAN_TYPE: return result.booleanValue;
				case XPathResult.UNORDERED_NODE_ITERATOR_TYPE:
					// not ensure the order.
					var ret = [], i = null;
					while ((i = result.iterateNext())) ret.push(i);
					return ret;
			}
			return null;
		default: throw(TypeError("$X: specified type is not valid type."));
	}
}