JavScript Alert box with line breaks code is given below--
<html>
<head>
<script type="text/javascript">
function disp_alert()
{
alert("Hello again! This is how we" + '\n' + "add line breaks to an alert box!");
}
</script>
</head>
<body>
<input type="button" onclick="disp_alert()" value="Display alert box" />
</body>
</html>