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
}
}