Allow user to extend the Array prototype

[ghost]

As-is, modifications to the array prototype will break the ability to create construction sites near the edges of rooms, where it would otherwise be allowed.

[o4kapuk]

@Dignissi could you please provide any reproduction code for the mentioned breaking?

[ghost]

@o4kapuk

Array.prototype.peek = function() { return this[this.length-1]; }
Game.rooms["E42S2"].createConstructionSite(1,43,STRUCTURE_WALL);

1,43 is a legal position (not adjacent to exit), for which createConstructionSite() is returning -7 with the prototype change, and 0 without

[madrang]

Extending Array with an enumerable property will make it show as a Key on all child arrays created later.
To fix this the engine should not change, but the function added should not be enumerable.

// Use the Object.defineProperty to make it not enumerable.
Object.defineProperty(Array.prototype, 'peek', {
    enumerable: false,  // this will make it not iterable
    get: function() { return this[this.length-1]; }
});