JavaScript 2D Array

Two dimensional array is commonly known as array of arrays. It is very useful in mathematics while working with matrix or grid. There are different approaches to create two dimensional array in JavaScript, these are -

Creating a 2D Array in JavaScript

A 2D array is created by nesting arrays within another array. Each nested array represents a "row," and each element within a row represents a "column."

1. Using Array Literal Notation - Most used

The basic method to create two dimensional array is by using literal notation [].

Syntax

const mat = [ [ num11, num12, ... ], [ num21, num22, ... ], ... ]

let mat = [
    [ 10, 20, 30 ],
    [ 40, 50, 60 ],
    [ 20, 50, 70 ]
];

console.log(mat);

[ [ 10, 20, 30 ], [ 40, 50, 60 ], [ 20, 50, 70 ] ]

2. Using Array.from() Method

The JavaScript Array from() method returns an Array object from any object with a length property or an iterable object.

Syntax

const mat = Array.from({ length: rows }, () => new Array(columns).fill(0));

const rows = 3;
const cols = 4;
const mat = Array.from({ length: rows }, () => new Array(cols).fill(0));
console.log(mat);

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

3. Using Nested For Loop

We can also use nested for loop to create a 2D array. The loop will iterate rows * cols times.

let mat = [];
let rows = 3;
let cols = 3;
let val = 0

for (let i = 0; i < rows; i++) {
    mat[i] = [];
    for (let j = 0; j < cols; j++) {
        mat[i][j] = val++;
    }
}

console.log(mat);

[ [ 0, 1, 2 ], [ 3, 4, 5 ], [ 6, 7, 8 ] ]

4. Using Array.fill() Method

In this approach, we will use the fill() method and map method for creating the two-dimensional array in JavaScript.

Example: This example shows the implementation of above-explained approach.

const rows = 3;
const cols = 4;

const mat = Array(rows).fill().map(() => Array(cols).fill(0));
               
console.log(mat);

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

Accessing Elements in a 2D Array

You can access elements in a 2D array using two indices: the row index and the column index. Remember that JavaScript uses zero-based indexing.

let mat = [
    [10, 20, 30],
    [40, 50, 60],
    [70, 80, 90]
];

console.log(mat[0][1]);
console.log(mat[2][0]);

20
70

Modifying Elements in a 2D Array

You can modify specific elements in a 2D array by accessing them with their indices and assigning a new value.

let mat = [
    [10, 20, 30],
    [40, 50, 60],
    [70, 80, 90]
];

mat[1][2] = 100;
console.log(mat);

[ [ 10, 20, 30 ], [ 40, 50, 100 ], [ 70, 80, 90 ] ]