Extendscript (JS): How to guard undefined object properties?

Question

Just picked up this Extendscript for a quick utility function. I can't seem to use any of the "usual" Javascript logic contstructs to test for undefined object properties.
Example:
typeof(app.activeDocument) === "undefined"
This is an *error* in Extendscript (Error 1302: No such element). I don't believe it should be, but if I'm supposed to do something different in Extendscript I am all ears.
Thank you
Edit: Now posted to the correct forum.

Answer 1

You could fix up something like:
var nicer_obj = function (obj) {
    var new_obj = {}
    for (key in obj) {
        if (obj.hasOwnProperty(key)) {
            try { new_obj[key] = obj[key]; } catch (err) {}
    return new_obj;
typeof nicer_obj(app).activeDocument; // 'undefined' or 'object'
For what it’s worth, I also think it’s really stupid and annoying that the built-in objects don’t behave at all like you’d expect typical ECMAScript objects to behave. Browsers used to have similar quirks (which is why everyone just uses jQuery), but many of those have been worked out by now.