Pomocí <img src=... onMouseOver='getMousePos(this, myFunction)'> chci spustit tuto funkci, ale hlásí mi to chybu

[pre]
  var getMousePos = function (that, myFunction = Null){
    var imgWidth = $(that).width();
    var imgHeight = $(that).height();
    var imgPosition = $(that).position();
    imgPosition.left = Math.round(imgPosition.left);
    imgPosition.right = imgPosition.left + imgWidth;
    imgPosition.top = Math.round(imgPosition.top);
    imgPosition.bottom = imgPosition.top + imgHeight;
    console.log(imgPosition);
    if ( mousePos.x > imgPosition.left &&
         mousePos.x < imgPosition.right &&
         mousePos.y > imgPosition.top &&
         mousePos.y < imgPosition.bottom
        )
       {
       console.log("You clicked in the image");
       if ( myFunction )
         {
         return myFunction();
         }
      }
  }
[/pre]

Nevíte co je špatně?