var percentX = left / objMark.offsetWidth;

var percentY = top / objMark.offsetHeight;

objBigBoxImage.style.left = -percentX * objBigBoxImage.offsetWidth ?+ "px";

objBigBoxImage.style.top = -percentY * objBigBoxImage.offsetHeight + "px";

這樣寫好像也能有同樣的效果，而且似乎好理解一點，是不是這樣會有什么問題呢