I am getting two different results for doing which I believe is the same thing in javascript with array push. Since I am new to javascript, I might be missing the big picture here.

Sample 1 -

class Test {

    constructor(){
        this.matrix = [];
    }

    createMatrix(){
        this.matrix.push([0,0,0]);
        this.matrix.push([0,0,0]);
        this.matrix.push([0,0,0]);
    }

    addNodes(x, y){
        this.matrix[x][y] = 1;
        this.matrix[y][x] = 1;
    }

    printMatrix(){
        return this.matrix;
    }
}

let test = new Test();
test.createMatrix();
console.log(test.printMatrix());
test.addNodes('1','2');
console.log(test.printMatrix());

O/p -

[ [ 0, 0, 0 ], [ 0, 0, 0 ], [ 0, 0, 0 ] ]

[ [ 0, 0, 0 ], [ 0, 0, 1 ], [ 0, 1, 0 ] ]

Sample 2 -

Replacing the createMatrix method with below one, gives me another result when trying to addNodes.

createMatrix(){
        let row = [0,0,0];
        this.matrix.push(row);
        this.matrix.push(row);
        this.matrix.push(row);
    }

O/p -

[ [ 0, 0, 0 ], [ 0, 0, 0 ], [ 0, 0, 0 ] ]

[ [ 0, 1, 1 ], [ 0, 1, 1 ], [ 0, 1, 1 ] ]

Please help me understand what I am missing out here, I want to achieve is o/p of sample 1 with the sample 2 code.