<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<script language="javascript">
var s=document.getElementById("main").childNodes;
alert(s.length);
</script>
</head>
<body>
<div id="main"><div id="div1">1231</div></div>
</body>
</html>
------解决方案--------------------
操作dom需要dom加载完毕才可以进行操作
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<script language="javascript">
window.onload = function(){
var s=document.getElementById("main").childNodes;
alert(s.length);
}
</script>
</head>
<body>
<div id="main"><div id="div1">1231</div></div>
</body>
</html>
或者
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
</head>
<body>
<div id="main"><div id="div1">1231</div></div>
<script language="javascript">
var s=document.getElementById("main").childNodes;
alert(s.length);
</script>
</body>
</html>