Typescript 2d array definition throws error

Question

I come from a strong JavaScript background attempting to learn TypeScript. I am encountering a problem that I know would work in JavaScript but is not working in TypeScript:

I am trying to initialize a class member with a matrix or 2d array of 5's; Here is my code:

private rows: number;
private cols: number;
private data: number[][];

constructor(rows: number, cols: number) {
    this.rows = rows;
    this.cols = cols;
    this.data = [];


    // init matrix with fives
    for (let i: number = 0; i < this.rows; i++) {
        this.data[i] = [];
        for (let j: number = 0; j < this.cols; i++) {
            this.data[i][j] = 5; // this is line 21
        }
    }
}

However, whenever I run the code and attempt to create a new instance of this class, I get an error on line 21 (shown above):

Uncaught TypeError: Cannot set property '0' of undefined

I've looked at this for quite a while, and it seems like other people do not have this problem. Does anybody know how to fix this?

Btw: I tried this same code in pure JS, and it worked fine without any errors.

Not a Typescript issue, you increment i în the second loop, should be j — Titian Cernicova-Dragomir
– Titian Cernicova-Dragomir, Commented Jul 18, 2018 at 18:55

Madhan Varadhodiyil · Accepted Answer · 2018-08-02 10:41:25Z

2

Seems like i is incremented in the second loop too.

for (let i: number = 0; i < this.rows; i++) {
    this.data[i] = [];
    for (let j: number = 0; j < this.cols; j++) { //j here
        this.data[i][j] = 5; // this is line 21
    }
}

edited Aug 2, 2018 at 10:41

answered Jul 18, 2018 at 19:04

Madhan Varadhodiyil

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Comments

vitomadio · Accepted Answer · 2018-07-18 19:23:43Z

0

I see you are declaring data variable as 2d array then you initialize it as 1d array after constructor. I think in typescript you shouldn't do that.

answered Jul 18, 2018 at 19:23

vitomadio

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