How do I subclass/extend TypedArrays in JavaScript?

Question

I'm writing an library in CoffeScript (so JS), and it is heavy math.. I really need to work with typed arrays (Float64Array) and all the performance they offer.

So what is the best way to extend the typed array functionality ??

Currently I'm doing it like functions:

Vector =
    create: (ag...) ->
        CGE2Point.create ag...
    dot: (i,j) ->
        i[0]*j[0] + i[1]*j[1]
    add: (i,j) ->
        @.create i[0]+j[0], i[1]+j[1]
    sub: (i,j) ->
        @.create i[0]-j[0], i[1]-j[1]
    mul: (s,v) ->
        @.create s * v[0], s * v[1]
    div: (s,v) ->
        @.create v[0] / s, v[1] / s

But would be really nice to have a Vector object, that inherits from the typed array. I know that the approach:

class Vector extends Float64Array

Create a class that do not have the full benefits the typed array Question about subclassing array , reading the following articles Dean Edwards suggests getting an object copy from an iframe, this other reference do it in other way Sorry Dean. But typed array do not have all that methods.

So, how is the right (or at least most elegant and performing) way to subclass the typed arrays ?? Or should I write all like functions ?

JavaScript is a Prototype based object model, not class based. — Incognito
– Incognito, Commented Sep 19, 2011 at 3:48
@Canesin the answers in this question can be very clarifying. — brandizzi
– brandizzi, Commented Sep 19, 2011 at 4:18
This question is ancient, but Arrays and TypedArrays are very distinct types. The links at the bottom of the question are about Arrays and aren't very relevant. — ZachB
– ZachB, Commented May 15, 2022 at 19:01

Pointy · Accepted Answer · 2023-06-15 13:34:10Z

5

Subclassing arrays in JavaScript is not really possible. Kangax (of Prototype fame) has written up a thorough elaboration of how/why it just doesn't work out.

edit — this answer is old. Modern JavaScript does provide the ability to subclass the built-in Array class properly.

edited Jun 15, 2023 at 13:34

answered Sep 19, 2011 at 3:31

Pointy

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5 Comments

CMCDragonkai Over a year ago

It appears you can make some progress using ES6 proxies, but performance drops significantly.

rfl890 Over a year ago

@CMCDragonkai

class SubArray extends Array {     randomElement() {         return this[Math.floor(Math.random() * this.length)]     } }

works for me.

Pointy Over a year ago

@rfl890 yea the answer is from 2011 :)

Bergi Over a year ago

Notice the question also is specifically asking about typed arrays, not Array. IIRC they were only introduced in ES6 (which was a big buzzword back then, and still a few years out in 2011), together with the possibility to subclass builtins.

Bergi Over a year ago

Notice the question also is specifically asking about typed arrays, not Array. IIRC they were only introduced in ES6 (which was a big buzzword back then, and still a few years out in 2011), together with the possibility to subclass builtins.

ZachB · Accepted Answer · 2022-05-15 18:58:58Z

2

It's possible to extends TypedArrays with class syntax.

class Vector extends Float64Array {
  constructor(i=0, j=0) {
    super([i, j])
  }
}

> new Vector()
Vector(2) [Float64Array] [0, 0]

Relevant part of the spec:

23.2.5 The TypedArray Constructors Each TypedArray constructor:

...

may be used as the value of an extends clause of a class definition. Subclass constructors that intend to inherit the specified TypedArray behaviour must include a super call to the TypedArray constructor to create and initialize the subclass instance with the internal state necessary to support the %TypedArray%.prototype built-in methods.

answered May 15, 2022 at 18:58

ZachB

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Comments

Trevor Burnham · Accepted Answer · 2011-09-19 14:46:05Z

1

As others have said: Alas, you can't subclass arrays (or typed arrays) in any meaningful way. But you can create an alias, e.g.

global.Vector = Float64Array

And you can add additional methods to the Float64Array prototype, e.g.

Float64Array::last = -> @[@length - 1]

It's not ideal from a modularity standpoint, but for a self-contained app, it's nice to be able to add that sort of syntactic sugar.

answered Sep 19, 2011 at 14:46

Trevor Burnham

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