对于不支持 getBoundingClientRect()的浏览器，可以通过其他手段取得相同的信息。一般来 说，right 和 left 的差值与 offsetWidth 的值相等，而 bottom 和 top 的差值与 offsetHeight 相等。综合上述，就可以创建出下面这个跨浏览器的函数:
function getElementLeft(element){
var actualLeft = element.offsetLeft;
var current = element.offsetParent;
while (current !== null){
actualLeft += current.offsetLeft;
current = current.offsetParent;
}
return actualLeft;
}
function getElementTop(element){
var actualTop = element.offsetTop;
var current = element.offsetParent;
while (current !== null){
actualTop += current. offsetTop;
current = current.offsetParent;
}
return actualTop;
}
function getBoundingClientRect(element) {
var scrollTop = document.documentElement.scrollTop;
var scrollLeft = document.documentElement.scrollLeft;
if (element.getBoundingClientRect) {
if (typeof arguments.callee.offset != "number") {
var temp = document.createElement("div");
temp.style.cssText = "position:absolute;left:0;top:0;"; document.body.appendChild(temp);
arguments.callee.offset = -temp.getBoundingClientRect().top - scrollTop; document.body.removeChild(temp);
temp = null;
}
var rect = element.getBoundingClientRect();
var offset = arguments.callee.offset;
return {
left: rect.left + offset,
right: rect.right + offset,
top: rect.top + offset,
bottom: rect.bottom + offset
};
} else {
var actualLeft = getElementLeft(element);
var actualTop = getElementTop(element);
return {
left: actualLeft - scrollLeft,
right: actualLeft + element.offsetWidth - scrollLeft,
top: actualTop - scrollTop,
bottom: actualTop + element.offsetHeight - scrollTop
}
}
}
