方法一
<!DOCTYPE html>
<html>
<head>
<title>Javascript中点击事件方法一</title>
</head>
<body>
<button id="btn">click</button>
<script type="text/javascript">
var btn = document.getElementById("btn");
btn.onclick=function(){
alert("hello world");
}
</script>
</body>
</html>
方法二
<!DOCTYPE html>
<html>
<head>
<title>Javascript中点击事件方法二</title>
</head>
<body>
<button id="btn">click</button>
<script type="text/javascript">
var btn = document.getElementById("btn");
btn.addEventListener(‘click‘,function(){
alert("hello wrold");
},false)
</script>
</body>
</html>
方法三
<!DOCTYPE html>
<html>
<head>
<title>Javascript中点击事件方法三</title>
<script type="text/javascript">
function test(){
alert("hello world");
}
</script>
</head>
<body>
<button id="btn" onclick="test()">click</button>
</body>
</html>
原文：https://www.cnblogs.com/sea-stream/p/10362815.html