<!DOCTYPE html>
<html>
<head>
<script>
var txt = "";
function message() {
try {
adddlert("Welcome guest!");
}
catch(err) {
txt = "There was an error on this page.\n\n";
txt += "Click OK to continue viewing this page,\n";
txt += "or Cancel to return to the home page.\n\n";
if(!confirm(txt)) {
document.location.href = "http://www.w3schools.com/";
}
}
}
</script>
</head>
<body>
<input type="button" value="View message" onclick="message()" />
</body>
</html>