What is a two-dimensional array?

JavaScriptJunior~1 min read

A two-dimensional array (or array of arrays) is a data structure in which each element is itself an array.

Put simply, it is a table: rows and columns, like in Excel or a matrix.

Example of a two-dimensional array:

javascript

const matrix = [
  [1, 2, 3],   // ← row 0
  [4, 5, 6],   // ← row 1
  [7, 8, 9]    // ← row 2
];

Here:

matrix[0] → [1, 2, 3] (the first row)
matrix[1][2] → 6 (an element from the second row, third column)

Visually:

javascript

[
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]

	0	1	2
0	1	2	3
1	4	5	6
2	7	8	9

How to access elements

javascript

console.log(matrix[0][0]); // 1
console.log(matrix[2][1]); // 8

The first index is the row, the second is the column.

How to iterate over all elements

With nested loops:

javascript

for (let i = 0; i < matrix.length; i++) {
  for (let j = 0; j < matrix[i].length; j++) {
    console.log(matrix[i][j]);
  }
}

i is the row number,
j is the column number.

Example use case:

Two-dimensional arrays are often used for:

storing tables and matrices of numbers;
representing game boards (for example, chess, tic-tac-toe);
storing coordinates (x, y);
working with images, pixels, grids, and so on.

Creating an empty two-dimensional matrix:

javascript

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

console.log(matrix);
/*
[
  [0, 0, 0, 0],
  [0, 0, 0, 0],
  [0, 0, 0, 0]
]
*/

In short:

Term	Meaning
Two-dimensional array	An array where each element is an array
Indexing	`[row][column]`
Example	`matrix[1][2] → 6`
Often used for	Tables, grids, coordinates, matrices

Summary: A two-dimensional array is a "table in code": an array made up of other arrays. It lets you conveniently store data as rows and columns.

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