JavaScript Array.concat() Method Example

The Array.concat() method is used to merge two or more arrays. This method does not change the existing arrays but instead returns a new array.

Syntax

var new_array = old_array.concat([value1[, value2[, ...[, valueN]]]])
Arrays and/or values to concatenate into a new array.

Examples

Example 1: Concatenating two arrays

The following code concatenates two arrays:
const letters = ['a', 'b', 'c'];
const numbers = [1, 2, 3];

letters.concat(numbers);
// result in ['a', 'b', 'c', 1, 2, 3]

Example 2: Concatenating three arrays

The following code concatenates three arrays:
const num1 = [1, 2, 3];
const num2 = [4, 5, 6];
const num3 = [7, 8, 9];

const numbers = num1.concat(num2, num3);

console.log(numbers); 
// results in [1, 2, 3, 4, 5, 6, 7, 8, 9]

Example 3: Concatenating values to an array

The following code concatenates three values to an array:
const letters = ['a', 'b', 'c'];

const alphaNumeric = letters.concat(1, [2, 3]);

console.log(alphaNumeric); 
// results in ['a', 'b', 'c', 1, 2, 3]

Example 4: Concatenating nested arrays

const num1 = [[1]];
const num2 = [2, [3]];

const numbers = num1.concat(num2);

console.log(numbers);
// results in [[1], 2, [3]]

// modify the first element of num1
num1[0].push(4);

console.log(numbers);
// results in [[1, 4], 2, [3]]

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