exceptions.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Using Exceptions</title>
</head>
<body onload="RunTest()">
<script language="JavaScript">
    <!--
    function InputException(msg) {
        this.val = msg;
        this.toString = function () {
            return "Input Exception in " + this.val
        };
    }

    function AreLetters(msg) {
        var input = msg;
        var re = new RegExp("[^a-zA-Z]");
        if(input.match(re)) {
            Oops = new InputException(input);
            throw Oops;
        }
    }

    function RunTest() {
        document.writeln("<h1>Using Exceptions</h1>");
        var input = prompt("Type Something", "");

        try {
            AreLetters(input);
            document.writeln("<p>You only see this if the exception is not thrown</p>");
        } catch (e) {
            document.writeln("<p>" + e.toString() + "</p>");
            document.close();
        }

        document.close();
    }
    //-->
</script>
</body>
</html>