1.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div id="div1" style=" 100px; height: 100px; padding:10px;border: 1px solid red;"></div>
<script>
window.onload = function () {
var oDiv = document.getElementById('div1')
console.log(oDiv.style.width) //100 样式宽
console.log(oDiv.clientWidth) //120 可视区宽 = 样式宽 + padding
console.log(oDiv.offsetWidth) //122 占位宽 = 可视区宽 + border
}
</script>
</body>
</html>