JavaScript Array.splice() - Insert, Remove, and Replace Elements

Understanding Array.splice()

Array.splice() is the most versatile mutating method. It can remove elements, insert elements, or replace elements at any position in the array — all in a single call.

Syntax

const removed = array.splice(start, deleteCount, item1, item2, ...);

• start — index where the operation begins
• deleteCount — how many elements to remove (0 to insert without removing)
• item1, item2, ... — elements to insert at the start position

Returns an array of removed elements.

Remove Elements

const arr = ["a", "b", "c", "d", "e"];
const removed = arr.splice(1, 2);
// arr: ["a", "d", "e"]
// removed: ["b", "c"]

Insert Elements

const arr = ["a", "c", "d"];
arr.splice(1, 0, "b");
// arr: ["a", "b", "c", "d"]

Replace Elements

const arr = ["a", "b", "x", "d"];
arr.splice(2, 1, "c");
// arr: ["a", "b", "c", "d"]

Negative Indices

Negative start values count from the end:

const arr = [1, 2, 3, 4, 5];
arr.splice(-2, 1);
// arr: [1, 2, 3, 5] (removed element at index -2 = index 3)

splice vs slice

	splice()	slice()
Mutates?	Yes	No
Returns	Removed elements	New sub-array
Can insert?	Yes	No

ES2023: toSpliced()

For immutable operations, use toSpliced():

const arr = ["a", "c", "d"];
const result = arr.toSpliced(1, 0, "b");
// result: ["a", "b", "c", "d"]
// arr: ["a", "c", "d"] (unchanged)