How do I override the constructor when extending Array class?

Question

I want to create a class named Matrix4 that extends Float32Array. I want to be able to override the Float32Array constructor with a constructor that creates an array of 16 elements (normally I would invoke new Float32Array(16), but now I just want new Matrix4).

// This function should override the Float32Array constructor
// And create a Matrix4 object with the size of 16 elements
var Matrix4 = function() {
    Float32Array.call(this, 16);
};

Matrix4.prototype = new Float32Array;

The error I get from this code is:

Constructor Float32Array requires 'new'

Hmm... I don't get that error. I get []. Is it possible that error is from somewhere else in your code? — jmargolisvt
– jmargolisvt, Commented Jan 27, 2017 at 15:08

lonesomeday · Accepted Answer · 2017-01-27 15:10:35Z

4

You can't extend built-in objects like Array or Float32Array using the old-fashioned pre-ES6 syntax. The only way to do it is with a class..extends statement:

class Matrix4 extends Float32Array {
    constructor() {
        super(16);
    }
}

let matrix = new Matrix4;
console.log(matrix.length); // 16

answered Jan 27, 2017 at 15:10

lonesomeday

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3 Comments

birgersp Over a year ago

I had no idea. I've been sticking to the old syntax but I guess it's time to adhere to the new... Thanks!

lonesomeday Over a year ago

@Birger There are still times when it's better to use the old style. But this isn't one of them!

birgersp Over a year ago

Do you mean Javascript classes in general, or just this particular class?

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