Obtain an HTML element's positon in body coordinates

If I have a nested HTML element called Div1 (a div that sits inside another div & that other div sits inside the body), how can I get Div1's x,y position from the body elements perspective maybe this is called window/screen position of a HTM开发者_如何学JAVAL element)?

Hope this makes sense :)

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function getWhere(node, top){
    top= top || document.body;
    var x= 0, y= 0;
    while(node){
        y+= node.offsetTop;
        x+= node.offsetLeft;
        node= node.offsetParent;
        if(node== top) break;
    }
    return [x, y];
}

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If you're using jQuery you can use offset to get the position relative to the document.

$(element).offset();

See: http://api.jquery.com/offset

Unfortunately I have no idea how to do this with pure js.