<html>
<head>
<title>HTML事件流</title>
<script>
var btn=document.getElementById("btn");
btn.onclick=showMessage();
function showMessage(){
alert("测试");
}
</script>
</head>
<body>
<div>
<input type="button" id ="btn" value="测试"/>
</div>
</body>
</html>btn.onclick=showMessage();这样写不行啊,会在刚进画面时弹框,点击按钮没有反应.