better_closest.js

(function(jQuery){

// This shortTermMemory will contain the last parsed simple selector.
// To be usefull it needs to be accessed faster than it would take to re-parse the selector.
// Selectors are to complex to serve as keys of a hash, and a bi-dimensional array would be too slow.
// I'm wondering if .data() would be fast enough for that purpose.
var shortTermMemory = [];
	
jQuery.fn.extend({
	closest: function( selector, context ) {
		var pos, closer = 0, re, split,
			// Fetch the last succesfully parsed selector 
			memory = shortTermMemory;
		// We are lookig for simple selectors such as "div", ".class" or "div.class"
		// If the selector has not previously been parsed
		if (selector != memory[0]) {
			// We will parse the selector and stop parsing as soon as possible, to do as few tests as possible
			split = selector.split('.');
			if (split.length < 3) {
				re = /^(?:[\w\u00c0-\uFFFF-]|\\.)*$/;
				// The selector begins with a tag (memory[1] = TAG) or with a "." (memory[1] = true)
				if (memory[1] = split[0] != ""? (re.test(split[0])? split[0] : false) : true) {
					// The second part of the selector is a class (memory[2] = class) or there is no second part (memory[2] = true)
					if(memory[2] = split[1]? (re.test(split[1])? " " + split[1] + " " : false) : true) {
						// If we arrived that far, we found a simple selector
						memory[0] = selector;
						shortTermMemory = memory;
					}
				}
			}
		}
		// If we haven't memorized the new selector, it wasn't simple
		if(selector != memory[0]) {
			// discard the memory
			memory[0] = false;
			// check for a position selector
			pos = jQuery.expr.match.POS.test( selector ) ? jQuery(selector) : null;
		}
		 

		return this.map(function(){
			var cur = this;
			while ( cur && cur.ownerDocument && cur !== context ) {
				// the selector was a position
				if ( pos? pos.index(cur) > -1 : (
				// the selector was simple
				memory[0]? ( (memory[1] === true || jQuery.nodeName(cur, memory[1])) && (memory[2] === true || (" " + cur.className + " ").indexOf(memory[2]) != -1))
				// The selector was complex
				: jQuery(cur).is(selector))) {
					jQuery.data(cur, "closest", closer);
					return cur;
				}
				cur = cur.parentNode;
				closer++;
			}
		});
	}
});

})(jQuery);