请教一个JS的问题，多谢回复！谢谢~

麻烦请问，这样写会导致内存泄露吗？多谢回复！ for examle:

var Pro = {
    doc : document,
    getLeftArrowEvent : function(){
	    //引入this，即整个对象为方便以后可能的引用
	    var is = this,
		    doc = is.doc,
		    leftArrow = doc.getElementById('leftArrow');
	    leftArrow.onmouseover = function(){
		    var th = is,
			    doc = th.doc,
			    leftArrow = doc.getElementById('leftArrow');
		    leftArrow.style.cursor = 'pointer';
	    };
	    leftArrow.onmouseout = function(){
		    var th = is,
			    doc = th.doc,
			    leftArrow = doc.getElementById('leftArrow');
		    leftArrow.style.cursor = '';
	    };
	    leftArrow = null;
    }
};