Arrays

An Array in JavaScript is a special type of object used to store ordered collections of values. These values can be of any type — numbers, strings, Booleans, objects, other arrays, or even functions. Arrays make it easy to store, access, and manipulate multiple values using indices.

Why Use Arrays?

Arrays are useful when you need to:

• Store multiple related values in a single variable.
• Perform operations on a collection of values (sorting, filtering, mapping, etc.).
• Iterate through data using loops.
• Keep your code organized and maintainable.

Example:

let fruits = ["apple", "banana", "orange"];
console.log(fruits); // ["apple", "banana", "orange"]

Essential Methods

Adding / Removing Elements

• push(...items): Add to the end. Returns new length.
• pop(): Remove from the end. Returns removed element.
• unshift(...items): Add to the start. Returns new length.
• shift(): Remove from the start. Returns removed element.
• splice(start, deleteCount, ...items): Add/remove at specific index.

arr.push(2); // [1, 'hello', { id: 1 }, 2]

arr.splice(1, 1, 'world'); // [1, 'world', { id: 1 }, 2]

Iterating / Transforming

forEach(callback): Run a function for each element.

arr.forEach(item => console.log(item));

map(callback): Create a new array with transformed elements.

let doubled = [1, 2, 3].map(x => x * 2); // [2, 4, 6]

filter(callback): Create a new array with elements passing a test.

let evens = [1, 2, 3, 4].filter(x => x % 2 === 0); // [2, 4]

reduce(callback, initialValue): Reduce to a single value.

let sum = [1, 2, 3].reduce((acc, x) => acc + x, 0); // 6

Searching / Sorting

find(callback): Return the first element matching the condition.

let found = arr.find(x => x === 'world'); // 'world'

includes(value): Check if a value exists.

arr.includes(1); // true

sort(compareFn): Sort in place. Use compareFn for numbers.

[3, 1, 2].sort((a, b) => a - b); // [1, 2, 3]

Other Useful Methods

• slice(start, end): Extract a portion (non-mutating).
• concat(...arrays): Merge arrays (non-mutating).
• join(separator): Convert array to string.

let part = arr.slice(1, 3); // ['world', { id: 1 }]

arr.join(', '); // '1, world, [object Object], 2'

Advanced Features

Spread Operator: Copy or merge arrays.

let copy = [...arr];             // Shallow copy
let merged = [...arr, ...[3, 4]];

• Destructuring: Extract elements into variables.

let [first, second] = arr; // first = 1, second = 'world'

Sparse Arrays: Gaps are filled with undefined.

let sparse = [1, , 3]; // [1, undefined, 3]