Arrays in JavaScript

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What is an Array?

An array is a special variable used to store multiple values in a single place.

const colors = ["red", "green", "blue"];

Think of it like a list or collection of items — each with an index starting from 0.

Why Use Arrays?

• Store related data (like names, scores, items)
• Loop through multiple values
• Perform operations like sorting, filtering, searching, etc.

Creating Arrays

const fruits = ["apple", "banana", "cherry"];
const numbers = [10, 20, 30, 40];
const mixed = ["text", 100, true, null];

You can also create an array using the Array() constructor:

const cars = new Array("Toyota", "Honda", "BMW");

Accessing Array Elements

console.log(fruits[0]); // apple
console.log(fruits[2]); // cherry

Modifying Array Elements

fruits[1] = "mango";
console.log(fruits); // ["apple", "mango", "cherry"]

Array Length

console.log(fruits.length); // 3

Adding & Removing Elements

push() — Add to end

fruits.push("grape");

pop() — Remove from end

fruits.pop();

unshift() — Add to beginning

fruits.unshift("orange");

shift() — Remove from beginning

fruits.shift();

Looping Through Arrays

for loop

for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

for...of

for (let fruit of fruits) {
  console.log(fruit);
}

forEach()

fruits.forEach(function(fruit) {
  console.log(fruit);
});

Common Array Methods

Method	Description	Example
push()	Add item to end	arr.push("new")
pop()	Remove last item	arr.pop()
shift()	Remove first item	arr.shift()
unshift()	Add item to start	arr.unshift("start")
indexOf()	Find index of an item	arr.indexOf("banana")
includes()	Check if item exists	arr.includes("apple")
join()	Join array to string	arr.join(", ")
slice()	Extract portion of array	arr.slice(1, 3)
splice()	Add/remove items	arr.splice(1, 2, "new")
concat()	Merge arrays	arr1.concat(arr2)
reverse()	Reverse the array	arr.reverse()
sort()	Sort the array	arr.sort()

Searching in Arrays

const pets = ["cat", "dog", "rabbit"];

console.log(pets.includes("dog")); // true
console.log(pets.indexOf("rabbit")); // 2

Array of Objects

const users = [
  { name: "Alice", age: 25 },
  { name: "Bob", age: 30 }
];
                                  
console.log(users[0].name); // Alice

Modern Array Methods (ES6+)

map() - transforms each item

const nums = [1, 2, 3];
const squared = nums.map(n => n * n); // [1, 4, 9]

filter() - keeps only matching items

const ages = [12, 18, 22, 15];
const adults = ages.filter(age => age >= 18); // [18, 22]

find() – returns first matching item

const found = ages.find(age => age > 18); // 22

Destructuring Arrays

Extract values into variables easily:

const cities = ["Delhi", "Mumbai", "Chennai"];
const [first, second] = cities;
                                    
console.log(first); // Delhi
console.log(second); // Mumbai

🧪 Practice Exercise:

Task:

1. Create an array of your favorite movies and print each using a loop.
2. Add and remove items using push() and pop().
3. Create an array of numbers and use map() to double each number.
4. Filter an array to find all even numbers.
5. Use splice() to replace an item in the array.