document.getElementById()为什么获取不了HTML元素节点? 调试的时候显示为null

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<script type="text/javascript">
var i = document.getElementById("in");
</script>
<body>
<a href="#" id="in">点我</a>
</body>
</html>

第1个回答  推荐于2017-09-13
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
<a href="#" id="in">点我</a>
<script type="text/javascript">
// 把脚本放到你要获取的元素的后面,在前面由于浏览器还没解释到这个对象,所以取不到.
var i = document.getElementById("in");
</script>
</body>
</html>本回答被提问者采纳
第2个回答  2011-11-20
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>

<body>
<a href="#" id="in">点我</a>

<script type="text/javascript">
var i = document.getElementById("in");
</script>
</body>
</html>
这样就可以不为null了,你上面的代码中,网页还没有加载完,就去寻找网页中的元素,是找不到的,