JavaScript reference

Array.prototype.splice

Removes, replaces or inserts elements in the middle of an array.

Available since: ES3

Syntax

array.splice(start, deleteCount, item1, /* … */)

Parameter	Type	Description
start	number	The position where the change starts. A negative one counts from the end.
deleteCount	number	Optional. How many elements to remove. All the rest by default.
item1, …	any	Optional. Elements to insert in place of the removed ones.

ArrayAn array of the removed elements.

Removing one element at an index:

const letters = ['a', 'b', 'c', 'd'];
letters.splice(1, 1);
 
console.log(letters);

Output:

[
  "a",
  "c",
  "d"
]

Inserting without removing — deleteCount is 0:

const letters = ['a', 'd'];
letters.splice(1, 0, 'b', 'c');
 
console.log(letters.join(''));

Output:

abcd

Replacing and getting the removed part:

const letters = ['a', 'b', 'c'];
const removed = letters.splice(1, 2, 'X');
 
console.log(removed.join(''), letters.join(''));

Output:

bc aX

Do not confuse it with slice(): splice() changes the original array, slice() does not. The non-mutating version is toSpliced().

Array methods — How to add and remove array elements in JavaScript: push, pop, shift, unshift, slice, splice, concat and join.