JavaScript Array splice()

let prime_numbers = [2, 3, 5, 7, 9, 11];

// replace 1 element from index 4 by 13
let removedElement = prime_numbers.splice(4, 1, 13);
console.log(removedElement);
console.log(prime_numbers);

// Output: [ 9 ]
//         [ 2, 3, 5, 7, 13, 11 ]

splice() Syntax

The syntax of the splice() method is:

arr.splice(start, deleteCount, item1, ..., itemN)

Here, arr is an array.

splice() Parameters

The splice() method takes in:

• start - The index from where the array is changed.
• deleteCount (optional) - The number of items to remove from start.
• item1, ..., itemN (optional) - The elements to add to the start index. If not specified, splice() will only remove elements from the array.

splice() Return Value

• Returns an array containing the deleted elements.

Note: The splice() method changes the original array.

Example 1: Using splice() method

let languages = ["JavaScript", "Python", "Java", "Lua"];

// replacing "Java" & "Lua" with "C" & "C++"
let removed = languages.splice(2, 2, "C", "C++");
console.log(removed); // [ 'Java', 'Lua' ]
console.log(languages); // [ 'JavaScript', 'Python', 'C', 'C++' ]

// adding elements without deleting existing elements
let removed1 = languages.splice(1, 0, "Java", "Lua");
console.log(removed1); // []
console.log(languages); // [ 'JavaScript', 'Java', 'Lua', 'Python', 'C', 'C++' ]

// removing 3 elements
let removed2 = languages.splice(2, 3);
console.log(removed2); // [ 'Lua', 'Python', 'C' ]
console.log(languages); // [ 'JavaScript', 'Java', 'C++' ]

Output

[ 'Java', 'Lua' ]
[ 'JavaScript', 'Python', 'C', 'C++' ]
[]
[ 'JavaScript', 'Java', 'Lua', 'Python', 'C', 'C++' ]
[ 'Lua', 'Python', 'C' ]
[ 'JavaScript', 'Java', 'C++' ]

Example 2: Using splice() for different deleteCount values

• If start > array.length, splice() does not delete anything and starts appending arguments to the end of the array.
• If start < 0, the index is counted from backward (array.length + start). For example, -1 is the last element.
• If array.length + start < 0, it will begin from index 0.

let languages = ["JavaScript", "Python", "Java", "Lua"];

// does not removes, only appends to the end
let removed = languages.splice(5, 2, "C++");
console.log(removed); // []
console.log(languages); // ["JavaScript", "Python", "Java", "Lua", "C++"]

// remove last element and add 3 more elements
let removed1 = languages.splice(-1, 1, "Swift", "Scala", "Go");
console.log(removed1); // [ "C++" ]
console.log(languages); // ["JavaScript", "Python", "Java", "Lua", "Swift", "Scala", "Go"]

Output

[]
["JavaScript", "Python", "Java", "Lua", "C++"]
[ 'C++' ]
["JavaScript", "Python", "Java", "Lua", "Swift", "Scala", "Go"]

Example 3: Using splice() for different start values

• If deleteCount is omitted or is greater than the number of elements left in the array, it deletes all elements from start to end of the array.
• If deleteCount is 0 or negative, no elements are removed. But, at least one new element should be specified.

let languages = ["JavaScript", "Python", "Java", "Lua"];

// removes everything from start
let removed = languages.splice(1);
console.log(removed); // [ "Python", "Java", "Lua" ]
console.log(languages); // [ "JavaScript" ]

// remove none & add 3 more element
let removed1 = languages.splice(1, -2, "Swift", "Scala", "Go");
console.log(removed1); // [ ]
console.log(languages); // [ "JavaScript", "Swift", "Scala", "Go" ]

Output

[ "Python", "Java", "Lua" ]
[ "JavaScript" ]
[ ]
["JavaScript", "Swift", "Scala", "Go"]

Recommended Readings:

• JavaScript Array.pop()
• JavaScript Array.push()