<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>title</title>
<script>
</script>
</head>
<body>
<input type="button" value="按钮" id="btn"/>
</body>
</html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>title</title>
<script>
//只要页面加载完毕了,再获取按钮
window.onload = function(){
document.getElementById("btn").onclick = function(){
alert("您好");
};
};
onload = function(){
document.getElementById("btn").onclick = function(){
alert("您好");
};
};
//扩展事件---->页面关闭之前触发的
window.onbeforeunload = function(){
alert("哈哈");
}
</script>
</head>
<body>
<input type="button" value="按钮" id="btn"/>
</body>
</html>