Check for optional parameter

by Andreas Renberg

HTML

<pre id="output"></pre>

JavaScript

function out()
{
    var args = Array.prototype.slice.call(arguments, 0);
    document.getElementById('output').innerHTML += args.join(" ") + "\n";
}

function optional(a) {
    out(a, (a === undefined) ? "not defined" : "defined");
}

optional("Hello world");
optional();
optional("");
optional(0);
optional(-1);
optional(null);
optional(undefined);