The $( ) function currently has a bottleneck when querying with a string (primitive).

I optimized the method and it gets a performance boost of 0-30% depending on browser:

http://jsperf.com/jquery-init-optimized

This is the current implementation of $( ). The first if clause checks for a nodeType property. When passing a String primitive this property check causes that string to be converted into a String wrapper object. Which slows everything down.

init: function( selector, context, rootjQuery ) {
  // ...
	// HANDLE: $(DOMElement) check first that selector is not a primitive
	if ( selector.nodeType ) { // ..
	}
	// Handle HTML strings
	if ( typeof selector === "string" ) {
	

The solution is to check first if selector is not a primitive (using typeof === 'object'). This has the effect that selector is not coerced to a string wrapper object. Typeof is fast.

init: function( selector, context, rootjQuery ) {
  // ...
	// HANDLE: $(DOMElement) check first that selector is not a primitive
	if ( typeof selector === "object" && selector.nodeType ) { // ..
	}
	// Handle HTML strings
	if ( typeof selector === "string" ) {
	

I'll create a pull request shortly.