Set Javascript Prototype Dynamically

Question

I am trying to set a prototype function dynamically using new Function(...). I have tried the following (es6):

export default class AI {

    constructor(algObj, player) {
        this.player = player;
        this.algObj = algObj;

        //create the shoot and placeShips prototypes form the this.algObj property
        this.prototype.initialize   = new Function(this.algObj.initialize);
        this.prototype.shoot        = new Function(this.algObj.shoot);
        this.prototype.placeShips   = new Function(this.algObj.placeShips);

        this.initialize();
    }
}

USE CASE: I have a micro service that stores algorithms as the resource which will then be passed into a simulator that battles 2 algorithms.

when I try this, this.prototype is undefined. The only reason I can think this might be the case is because the AI object is not fully defined until after the constructor is done executing.

How would I go about setting a prototype function like I am trying to do here?

UPDATE:

this.__proto__.initialize   = new Function(this.algObj.initialize);
this.__proto__.shoot        = new Function(this.algObj.shoot);
this.__proto__.placeShips   = new Function(this.algObj.placeShips);

There will by one AI instance per game and there will be multiple games per simulation. — frankgreco, Jun 12 '16 at 17:19
You now have two questions: about prototype being undefined, and about assigned functions which are anonymous. Please don't mix these into one question: ask a separate one for each. — trincot, Jun 12 '16 at 17:21
I will open another question for the anonymous function question — frankgreco, Jun 12 '16 at 17:27
You [must not overwrite prototype methods from inside the constructor](http://stackoverflow.com/q/28255957/1048572). — Bergi, Jun 12 '16 at 20:48
Note: if performance is critical, `new Function` isn't a good idea. If this bit isn't performance-intensive, you might be able to get away with it. — gcampbell, Jun 12 '16 at 22:15

score 3 · Accepted Answer · answered Jun 12 '16 at 17:26

3

When the constructor is invoked you already have an instance of the object you're creating, and thus you can simply modify the instance's methods without touching the prototype:

export default class AI {

    constructor(algObj, player) {
        this.player = player;
        this.algObj = algObj;

        //create the shoot and placeShips prototypes form the this.algObj property
        this.initialize   = new Function(this.algObj.initialize);
        this.shoot        = new Function(this.algObj.shoot);
        this.placeShips   = new Function(this.algObj.placeShips);

        this.initialize();
    }
}

answered Jun 12 '16 at 17:26

Schlaus

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This works! So are the 3 functions then added to AI.prototype – frankgreco Jun 12 '16 at 17:30
1

@Frank No, they are added to the instance the constructor is, well, constructing. The prototype remains untouched. – Schlaus Jun 12 '16 at 17:33
@jfriend00: Apparently `algObj` contains code strings, otherwise it wouldn't work. Why it does that, and whether that is a good idea, we better discuss elsewhere. – Bergi Jun 12 '16 at 20:49
Yea I use new Function because I'm passing in a string. – frankgreco Jun 12 '16 at 20:59

Set Javascript Prototype Dynamically

1 Answers1