获取元素相对于页面的偏移值_getElementRect = function(e) {	var bounds;	try { bounds = e.getBoundingClientRect(); } // this can fail on disconnected DOM elements in IE9	catch (err) { bounds = {top: e.offsetTop, left: e.offsetLeft, width:e.offsetWidth, height:e.offsetHeight}; }	var offX = (window.pageXOffset || document.scrollLeft || 0) - (document.clientLeft || document.body.clientLeft || 0);	var offY = (window.pageYOffset || document.scrollTop || 0) - (document.clientTop  || document.body.clientTop  || 0);	var styles = window.getComputedStyle ? getComputedStyle(e,null) : e.currentStyle; // IE <9 compatibility.	var padL = parseInt(styles.paddingLeft)+parseInt(styles.borderLeftWidth);	var padT = parseInt(styles.paddingTop)+parseInt(styles.borderTopWidth);	var padR = parseInt(styles.paddingRight)+parseInt(styles.borderRightWidth);	var padB = parseInt(styles.paddingBottom)+parseInt(styles.borderBottomWidth);	// note: in some browsers bounds properties are read only.	return {		left: bounds.left+offX+padL,		right: bounds.right+offX-padR,		top: bounds.top+offY+padT,		bottom: bounds.bottom+offY-padB	}}