带有换行的警告框
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>滴答编程(dida100.com)</title>
</head>
<body>
<p>点击按钮在弹窗中使用换行。</p>
<button onclick="myFunction()">点我</button>
<p id="demo"></p>
<script>
function myFunction(){
alert("Hello\nHow are you?");
}
</script>
</body>
</html>