目的：点击button按钮弹出消息
知识点：window.onload事件是在网页加载完后才执行，如果不在window.onload事件中写事件会处错误。
如以下代码报 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>
<script>
var oBtn = document.getElementById(‘btn1‘);
oBtn.onclick = function()
{
alert(‘not onload‘);
}
</script>
</head>
<body>
<input id="btn1" type="button"/>
</body>
</html>
正确写法：只要在外层套一个window.onload = function(){};即可
<!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>
<script>
window.onload = function()
{
var oBtn = document.getElementById(‘btn1‘);
oBtn.onclick = function()
{
alert(‘onload‘);
}
}
</script>
</head>
<body>
<input id="btn1" type="button"/>
</body>
</html>
时间： 2025-01-03 16:34:04