style.width,clientWidth,offsetWidth
document
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<html><head><meta charset="utf-8"><title>document</title><style>div{ padding:40px 50px;}#div1 { background:red;}#div2 { background:blue; position:relative;}#div3 { background:orange;}</style><script type="text/javascript"> window.onload = function() { var oDiv1 = document.getElementById('div1'); /* style.width:样式宽(带单位) clientWidth: 可视区宽(样式宽+padding 不带单位) offsetWidth:占位宽(样式宽+padding+border 不带单位) */ alert(oDiv1.style.width + ' ' + oDiv1.clientWidth + ' ' + oDiv1.offsetWidth); } </script></head><body id="body"> <div id="div1" style="width:100px; height:100px; padding:10px; margin:10px; border:1px solid red;"></div></body></html>