Predefined Exceptions in JavaScript

<script type="text/javascript">
try {
    eval("a ++ b");        //causes SyntaxError
} catch (oException) {
    if (oException instanceof SyntaxError) {
        alert("Syntax Error: " + oException.message);
    } else {
        alert("An unexpected error occurred: " + oException.message);
    }
}
</script>