Get element offset

/*
 Get ellement offset.
 @constructor
 @param {node} element - needs node element
 
 @return {Object} - Top and left element offsets
 @returnParams {Number} Object.top - top offset
 @returnParams {Number} Object.left - left offset
 */
 
var getElementOffset = function (element){
  if (!(element instanceof HTMLElement)){
    return 'Value is not node!'
  }
  
  var de = document.documentElement,
      box = element.getBoundingClientRect(),
      top = box.top + window.pageYOffset - de.clientTop,
      left = box.left + window.pageXOffset - de.clientLeft;
  if(isNumeric(top) && isNumeric(left)){
    return { top: top, left: left }; 
  } else {
    return 'Problem with values'
  }
}

// Helper
function isNumeric(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}