Arrays and Objects

An array is an ordered list of values, indexed from 0:

const fruits = ["apple", "banana", "cherry"];
console.log(fruits[0]); // "apple"
console.log(fruits.length); // 3

An object is a collection of named properties — think of it as a labeled record instead of a numbered list:

const book = { title: "Dune", year: 1965, pages: 412 };
console.log(book.title); // "Dune"

Arrays come with powerful built-in methods that avoid writing manual loops for common transformations:

• map builds a new array by transforming every item: [1,2,3].map(n => n * 2) → [2,4,6]
• filter builds a new array keeping only items that pass a test: [1,2,3,4].filter(n => n % 2 === 0) → [2,4]
• find returns the first item that passes a test, or undefined if none do: [1,2,3].find(n => n > 1) → 2

All three take a function as an argument and never modify the original array — they return a new value instead, which makes your code easier to reason about.

Destructuring is a shorthand for pulling values out of arrays or objects into their own variables:

const [first, second] = fruits;         // first = "apple", second = "banana"
const { title, year } = book;           // title = "Dune", year = 1965

This is especially common when working with function parameters that are objects, e.g. function printBook({ title, year }) { ... }, since it avoids repeatedly writing book.title, book.year.