[转] [备忘]原生JS获取dom的左下坐标

<script>
function getElementPos(elementId) {
  
    var ua = navigator.userAgent.toLowerCase();
    var isOpera = (ua.indexOf('opera') != -1);
    var isIE = (ua.indexOf('msie') != -1 && !isOpera); // not opera spoof
  
    var el = document.getElementById(elementId);
  
    if(el.parentNode === null || el.style.display == 'none') 
    {
        return false;
    }
  
    var parent = null;
    var pos = [];
    var box;
  
    if(el.getBoundingClientRect)    //IE
    {
        box = el.getBoundingClientRect();
        var scrollTop = Math.max(document.documentElement.scrollTop, document.body.scrollTop);
        var scrollLeft = Math.max(document.documentElement.scrollLeft, document.body.scrollLeft);
  
        return {x:box.left + scrollLeft, y:box.top + scrollTop};
    }
    else if(document.getBoxObjectFor)   // gecko
    {
        box = document.getBoxObjectFor(el);
            
        var borderLeft = (el.style.borderLeftWidth)?parseInt(el.style.borderLeftWidth):0;
        var borderTop = (el.style.borderTopWidth)?parseInt(el.style.borderTopWidth):0;
  
        pos = [box.x - borderLeft, box.y - borderTop];
    }
    else    // safari & opera
    {
        pos = [el.offsetLeft, el.offsetTop];
        parent = el.offsetParent;
        if (parent != el) {
            while (parent) {
                pos[0] += parent.offsetLeft;
                pos[1] += parent.offsetTop;
                parent = parent.offsetParent;
            }
        }
        if (ua.indexOf('opera') != -1 
            || ( ua.indexOf('safari') != -1 && el.style.position == 'absolute' )) 
        {
                pos[0] -= document.body.offsetLeft;
                pos[1] -= document.body.offsetTop;
        } 
    }
         
    if (el.parentNode) { parent = el.parentNode; }
    else { parent = null; }
   
    while (parent && parent.tagName != 'BODY' && parent.tagName != 'HTML') 
    { // account for any scrolled ancestors
        pos[0] -= parent.scrollLeft;
        pos[1] -= parent.scrollTop;
   
        if (parent.parentNode) { parent = parent.parentNode; } 
        else { parent = null; }
    }
    return {x:pos[0], y:pos[1]};
}
</script>