Mutator Methods (push, pop, shift, unshift, splice, sort, reverse, fill, copyWithin)

Mutator methods modify the original array. They are used to add, remove, reorder, or fill elements in place.

Common Mutator Methods

Method	Description
push()	Adds one or more elements to the end. Returns new length.
pop()	Removes the last element. Returns removed element.
shift()	Removes the first element. Returns removed element.
unshift()	Adds one or more elements to the beginning. Returns new length.
splice()	Adds, removes, or replaces elements at a specified index.
sort()	Sorts the array in place (optionally with compare function).
reverse()	Reverses the order of elements in place.
fill()	Fills a range of elements with a static value.
copyWithin()	Copies a sequence of elements to another position within the array.

Code Example

let arr = [1, 2, 3, 4];

arr.push(5); // arr = [1, 2, 3, 4, 5]
arr.pop(); // arr = [1, 2, 3, 4]
arr.unshift(0); // arr = [0, 1, 2, 3, 4]
arr.shift(); // arr = [1, 2, 3, 4]

arr.splice(1, 2, "a", "b"); // arr = [1, 'a', 'b', 4]
arr.sort(); // arr = [1, 4, 'a', 'b'] (lexicographic)
arr.reverse(); // arr = ['b', 'a', 4, 1]

arr.fill(0, 1, 3); // arr = ['b', 0, 0, 1]
arr.copyWithin(0, 2, 4); // arr = [0, 1, 0, 1]