How to Add 2 Arrays Together in JavaScript
Feb 7, 2023
To add 2 arrays together in JavaScript, we recommend using the concat() function.
The concat() function returns a new array that consists of the two given arrays together.
const array = [1, 2, 3];
const array2 = [4, 5, 6];
const array3 = array.concat(array2); // [1, 2, 3, 4, 5, 6]
array3 === array; // falsepush() with spread operator
You can also use the push() method with the spread operator.
This approach modifies the array in place instead of creating a new array.
const array = [1, 2, 3];
const array2 = [4, 5, 6];
array.push(...array2); // [1, 2, 3, 4, 5, 6]Note: Be careful about using this approach with potentially huge arrays. This can cause a stack overflow error if array2 is massive.
const array = [];
const array2 = Array(10_000_000).fill(null);
// RangeError: Maximum call stack size exceeded
array.push(...array2);Using Immutable Patterns
You can also use the spread operator as an alternative to concat() to create a new array as follows.
This approach is syntactically neater, and gives you more flexibility in constructing the new array.
const array = [1, 2, 3];
const array2 = [4, 5, 6];
const array3 = [...array, ...array2]; // [1, 2, 3, 4, 5, 6]
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