该valueOf()函数接受一个Number对象，并返回由给定对象包装的数字（原始）。
其语法如下
num.valueOf(num);
<html>
<head>
<title>JavaScript Example</title>
</head>
<body>
<script type="text/javascript">
var num = 215;
result = num.toString(16);
document.write("Result: " + result);
</script>
</body>
</html>输出结果
Result: d7
<html>
<head>
<title>JavaScript Example</title>
</head>
<body>
<script type="text/javascript">
var num = 215;
result = num.toString(16);
document.write("Result: " + result);
document.write("<br>");
document.write("Result: " + num.valueOf(0));
document.write("<br>");
document.write("Result: " + num.valueOf(-16));
document.write("<br>");
document.write("Result: " + num.valueOf());
document.write("<br>");
var dat = 0/0;
document.write("Result: " + dat.valueOf(16));
</script>
</body>
</html>输出结果
Result: d7 Result: 215 Result: 215 Result: 215 Result: NaN