[amt35]

(function() {
    function _$(els) {
	    this.elements = []; 
		this.elements = Array.prototype.slice.call(document.querySelectorAll(els));
        return this;
    }
	_$.prototype ={
	size: function() {
	  alert('size:'+this.elements.length);
	  return this;
	}
	};
	window.$ = function() { return new _$(arguments); }
})();

Использование $('#test').size();