<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta charset="utf-8">
<title>test</title>
</head>
<body>
<button>1111</button>
<button>2222</button>
<button>3333</button>
</body>
<script>
for(var i=0;i<3;i++){
document.getElementsByTagName("button")[i].onclick=function(){
alert(i);
}
}
</script>
</html>
为什么点击每个按钮都会弹出3??