How to instantiate a class object with a 2 dimensional array?

Question

I'm trying to insantiate an object with a 2 dimensional array but the following code doesn't seem to work:

class Board {
  constructor(row,col){
    this.board=[];
    for (var i=0; i<row; i++){
      for (var y=0; y<col; y++){
        this.board[i][y]=0;
      }
    }
  }
}

var board = new Board(10,10);

https://jsbin.com/worepeb/edit?js,console

Answer 1

You need to init the sub-array before you can fill it with numbers - this.board[i] = [];:

class Board {
  constructor(row,col){
    this.board=[];
    for (var i=0; i<row; i++){
      this.board[i] = []; // init this.board[i]
      for (var y=0; y<col; y++){
        this.board[i][y]=0;
      }
    }
  }
}

var board = new Board(10,10);

console.log(board);

You can also use Array.from() to init the board:

class Board {
  constructor(row,col){
    this.board = Array.from({ length: row }, () => 
      Array.from({ length: col }, () => 0)
    );
  }
}

const board = new Board(10,10);

console.log(board);