JS - Same function in each object in array

Question

I've got 2d array of object like chessboard.

You can get object by data.field(x,y); (object are stored inside 2d array of objects)

I want each of fields to have functions: top, bottom, left, right that will return neighbour field.

For example data.field(3,3).top().left().bottom().name would return name of field(4,3).

But: Have I to declare those function for each of objects? I mean, for example on 8x8 field that would be 64 instances of the same function:

data.field(0,0).top = function(){...}
data.field(0,1).top = function(){...}
...

Ofc I can easily declare them inside loop, but its pure waste of memory and I'm sure its not the way to do it. Is it possible to declare this functions only once to be available inside every object returned by field(x,y) function?

T.J. Crowder · Accepted Answer · 2013-03-04 17:25:56Z

1

Is it possible to declare this functions only once to be avaliable inside every object returned by field(x,y) function?

Absolutely:

function top() {
    // ...do your thing, using `this`
}

data.field(0,0).top = top;

When top is called as part of an expression retrieving it from the field(0,0) object, within the call to top, this will be the field(0,0) object. And similarly for field(0,1), etc.

More (on my blog):

Mythical Methods

Now, that assumes that for whatever reason, you already have the field(0,0) and such objects (perhaps they're created by code you don't control). If you control the code, you can do this via the prototype chain instead:

function Field() {
}
Field.prototype.top = function() {
    // ...do your top thing, using `this`
};

...and when creating your fields:

yourField = new Field();

So it depends on what data.fields(0,0) is and where you get it.

answered Mar 4, 2013 at 17:25

T.J. Crowder

1.1m201 gold badges2k silver badges2k bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

T.J. Crowder Over a year ago

@alex23: What's not OOP about attaching behaviors to objects?

OPOPO Over a year ago

Do I need to still do it for each of fields? data.field(0,0).top = top; data(0,1).top = top and so on?

T.J. Crowder Over a year ago

@OPOPO: You do with the above, let me post an alternative. But note that although you're doing the assignment, you're not duplicating the function, you're just reusing it.

Halcyon Over a year ago

@alex23 you can do OOP without Classes, even without prototypes because JavaScript is that awesome.

Halcyon · Accepted Answer · 2013-03-04 17:28:41Z

0

If you want to conserve memory you should look at prototypes. They're like Classes in Object Oriented languages, so there is an opportunity for memory optimization.

var Field = function() {}; // this is your constructor
Field.prototype.top = function () { /* .. */
    return this; // return the field so you can do chaining: field.top().left();
};
Field.prototype.left = function () { /* .. */
    return this;
};
/* .. */
var field = new Field();
data.set(0, 0, field);
data.field(0, 0).top().left();

answered Mar 4, 2013 at 17:28

Halcyon

57.7k10 gold badges93 silver badges131 bronze badges

Collectives™ on Stack Overflow

JS - Same function in each object in array

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related