offsetWidth表示对对象的可见宽度

offsetWidth=width+padding+border

而offsetLeft是盒子边缘到上一级盒子内边框的距离，所以跟margin值有关，与border和padding没有关系。 

offsetLeft=left+margin

*{margin: 0;padding: 0;}#div1{width: 400px;height: 400px;background-color: #ccc;border: 2px solid #999;padding:11px;margin: 22px;}#div2{width: 100px;height: 100px;background-color: red;border: 1px solid #999;padding:10px;margin: 19px;}</style><script type="text/javascript">window.οnlοad=function(){var aDiv=document.getElementById('div1');var aDiv2=document.getElementById('div2')alert(aDiv2.offsetWidth)   //122=100+10+10+1+1=width+padding+borderalert(aDiv2.offsetHeight)  //122=100+10+10+1+1=height+padding+borderalert(aDiv2.offsetLeft)  //54 = 2+11+22+19= div1的border+div1的padding+div1的margin+div2的marginalert(aDiv2.offsetTop)  //54}</script>