Array .push() / pop() / shift() / unshift()

// Adds one or more elements to the end of the array.
array.push(element1, element2, ...);

// Removes and returns the last element of the array.
var removed = array.pop();

// Adds one or more elements to the beginning of the array.
array.unshift(element1, element2, ...);

// Removes and returns the first element of the array.
var removed = array.shift();

var fruits = ["apple", "orange"];

// Adds an element to the end.
fruits.push("grape");
console.log(fruits); // Outputs "apple,orange,grape".

// Removes the last element.
var last = fruits.pop();
console.log(last); // Outputs "grape".
console.log(fruits); // Outputs "apple,orange".

// Adds an element to the beginning.
fruits.unshift("banana");
console.log(fruits); // Outputs "banana,apple,orange".

// Removes the first element.
var first = fruits.shift();
console.log(first); // Outputs "banana".
console.log(fruits); // Outputs "apple,orange".

These four methods are the most fundamental ways to manipulate elements at the end and beginning of an array. push() and pop() operate on the end, while unshift() and shift() operate on the beginning. All four are mutating methods that modify the original array directly.

push() can add multiple elements at once by passing them as comma-separated arguments, and its return value is the new length of the array. pop(), on the other hand, takes no arguments and returns the removed element itself. These two methods are commonly used together to implement a stack (last-in, first-out) data structure.

To add or remove elements in the middle of an array, use splice().