JavaScript common method to multiple existing constructors

Question

I am rather new to Javascript's way of dealing with constructors,methods and prototypes.

I want to create two constructors that have many different custom methods, but also have some methods in common. Currently I do things like this:

function PlayerWhite(n,s) {     this.name = n; this.state = s;}

function PlayerBlack(n,c) {     this.name = n; this.county = c; }

PlayerWhite.prototype.showCounty = function() { alert(this.county);}

PlayerBlack.prototype.showState = function() { alert(this.state);}

PlayerWhite.prototype.showName = function() {   alert(this.name); }

PlayerBlack.prototype.showName = function() {   alert(this.name); }

So the contents of the "showName" method is identical for both constructors. The code for "showName" may change and it will be the same for both, so I dont want to do double edits each time I will do an update to the showName method.

Of course, I could use just 1 constructor (function Player), call it twice to build each of the two objects, then assign the common methods to each object and then apply the distinct methods to each object using prototype , but what if I already wrote hundreds of lines of code and I have many objects created from the PlayerBlack and PlayerWhite constructors and I just want to add a new method that could be used between all the existing objects created through PlayerBlack or PlayerWhite?

I tried something like this, but it doesnt work:

PlayerWhite.prototype.showName, 
PlayerBlack.prototype.showName = function() {   alert(this.name); }

I am looking for a solution that would work in nodeJS.

Radek Pech · Accepted Answer · 2016-01-14 14:10:02Z

2

To share a method, assign it like this:

PlayerWhite.prototype.showName = function() {   alert(this.name); }
PlayerBlack.prototype.showName = PlayerWhite.prototype.showName;

To create shared parent:

Shared = function() { }

//here define shared methods
Shared.prototype.showName = function() { alert(this.name); }

PlayerWhite.prototype = new Shared();
PlayerBlack.prototype = new Shared();

//here define non-shared methods
PlayerWhite.prototype.showCounty = function() { alert(this.county);}
PlayerBlack.prototype.showState = function() { alert(this.state);}

edited Jan 14, 2016 at 14:10

answered Jan 14, 2016 at 13:55

Radek Pech

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2 Comments

NVG Over a year ago

Excellent. This is exactly what I was looking for.

Radek Pech Over a year ago

@NVG added correct way to share methods with a parent.

Lashus · Accepted Answer · 2016-01-14 13:59:18Z

0

You are looking for simply inheriting methods. Please take a look at MDN for further explanation - it is really nicely explained out there.

https://developer.mozilla.org/pl/docs/Web/JavaScript/Inheritance_and_the_prototype_chain

Also - if you are looking forward to using nodeJs please take a look at it's "modules".

https://nodejs.org/api/modules.html

You can combine both methods ending up in something like this:

var BaseModel = require('PATHTOBASEMODEL/base_model');

ExtendedModel = Object.create(BaseModel);

ExtendedModel.prototype.yourFunction = function () { /* ... */ };

module.exports = ExtendedModel;

answered Jan 14, 2016 at 13:59

Lashus

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2 Comments

NVG Over a year ago

I appreciate your answer, but it seems easier to do it natively, as Radek Pech answered below.

Lashus Over a year ago

Easier doesn't mean better. You have code hard to maintain using "native" way (you can't call it native though because both are) and you have code duplicates. If you want to inherit 50 methods you will write same code every time? The proper way actually is to declare basic abstract class Player and two players (or even N players) inheriting from that class.

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