Missing methods in extendscript - differences between machines and installations

Per Justin T's reply, because ExtendScript is based on an older or stripped down of Javascript, you may not have some functions. I added Array.map with this:

Array.prototype.map = function (callbackFn) {
    var arr = [];
    for (var i = 0; i < this.length; i++) {
        /* call the callback function for every value of this array and       push the returned value into our resulting array
        */
        arr.push(callbackFn(this[i], i, this));
    }
    return arr;
}

Hey guys,

After asking around in the Beta forum as well, I've gotten a very interesting explanation that I wanted to share here as well.
As it turns out, Adobe's own Panels can add functionality to your codebase as well.

We received the following info:
Launching 'Learning' adds in Array. indexOf, which other jsx scripts can see and access.
Launching 'Libraries' panel adds Array.indexOf, Array. filter, and Array .map (which again is accessible from your own scripts).
All of them will also add JSON.

So, depending on which panels you load in at start, or later, as soon as one of these are loaded you are adding functionality untill you close AE again. So, while it is true in my case that the extra methods were added by "external code", it was in fact "external code" from Adobe themselves, it appears.

Very interesting and explains a lot!

If I remember correctly, filter and map are not part of ExtendScript by default.

If on a machine filter and map are available, I guess on this machine you have some scripts installed and executed on startup that add polyfills for these functions.