JavaScript Array Methods

Array Properties and Methods

JavaScript provides various array properties and methods:

.length: Get the number of elements:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
console.log(fruits.length); // Output: 4

.sort(): Sort elements in ascending order:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
console.log(fruits.sort()); 
// Output: Array(4) [ "Apple", "Banana", "Mango", "Orange" ]

Looping Through an Array

Using for loop:

const fruits = ["Cherry", "Mango", "Orange"];
for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}
// Output: 
Cherry
Mango
Orange

Using forEach():

fruits.forEach(fruit => console.log(fruit));
// Output: 
Cherry
Mango
Orange

Adding Elements to an Array

Using push():

const fruits = ["Apple", "Banana", "Cherry"];
fruits.push("Mango");
console.log(fruits); 
// Output: ["Apple", "Banana", "Cherry", "Mango"]

Using length property:

const fruits = ["Apple", "Banana", "Cherry"];
fruits[fruits.length] = "Mango";
console.log(fruits);
// Output: ["Apple", "Banana", "Cherry", "Mango"]

Using unshift() Method:

const fruits = ["Apple", "Banana", "Cherry"];
fruits.unshift("Lemon");
console.log(fruits); // Output: ["Lemon", "Apple", "Banana", "Cherry"]

Removing Elements to an Array

Using splice() method:

The splice(1, 1) method removes 1 element at index 1 ("Banana") from the array, leaving ["Apple", "Cherry"].

const fruits = ["Apple", "Banana", "Cherry"];
fruits.splice(1, 1);
console.log(fruits); // Output: ["Apple", "Cherry"]

Using slice() method:

The slice(1, 3) method extracts elements from index 1 to 2, returning ["Banana", "Cherry"] without modifying the original array.

const fruits = ["Apple", "Banana", "Cherry"];
const slicedFruits = fruits.slice(1, 3);
console.log(slicedFruits); // Output: ["Banana", "Cherry"]

Using pop() method:

The pop() method removes and returns the last element ("Cherry") from the array, modifying the original array.

const fruits = ["Apple", "Banana", "Cherry"];
const removedFruit = fruits.pop();
console.log(removedFruit); // Output: Cherry
console.log(fruits); // Output: ["Apple", "Banana"]

Using shift() method:

The shift() method removes and returns the first element ("Apple") from the array, modifying the original array.

const fruits = ["Apple", "Banana", "Cherry"];
const firstFruit = fruits.shift();
console.log(firstFruit); // Output: Apple
console.log(fruits); // Output: ["Banana", "Cherry"]

Recognizing an Array

Use Array.isArray() to check if a variable is an array:

const fruits = ["Apple", "Banana", "Cherry"];
console.log(Array.isArray(fruits)); // Output: true
const person = { firstName: "John", lastName: "Doe" };
console.log(Array.isArray(person)); // Output: false

Merging Arrays

concat() Method

const girls = ["Cecilie", "Lone"];
const boys = ["Emil", "Tobias", "Linus"];
const children = girls.concat(boys);
console.log(children); // Output: ["Cecilie", "Lone", "Emil", "Tobias", "Linus"]

Copying Elements

copyWithin() Method

const numbers = [1, 2, 3, 4, 5];
numbers.copyWithin(2, 0);
console.log(numbers); // Output: [1, 2, 1, 2, 3]

Flattening Arrays

flat() Method

const nestedArray = [[1, 2], [3, 4], [5, 6]];
console.log(nestedArray.flat()); // Output: [1, 2, 3, 4, 5, 6]

flatMap() Method

const numbers = [1, 2, 3];
console.log(numbers.flatMap(n => [n, n * 10])); // Output: [1, 10, 2, 20, 3, 30]