[原]js获取dom元素的实际位置及相对坐标

关键API：

Element.getBoundingClientRect()

mdn：https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect

用法：

var rect = element.getBoundingClientRect();
console.log(rect.top, rect.right, rect.bottom, rect.left);

获取相对位置：

var bodyRect = document.body.getBoundingClientRect(),
    elemRect = element.getBoundingClientRect(),
    offset   = elemRect.top - bodyRect.top;

alert('Element is ' + offset + ' vertical pixels from <body>');

参考网址：http://stackoverflow.com/questions/442404/retrieve-the-position-x-y-of-an-html-element

我只是个搬运工，一起学习了~