JavaScript Tutorial
Arrays store ordered lists of values and are one of the most used data structures in JavaScript.
Once you know the basics, methods like map, filter, and reduce become powerful tools.
Most apps work with lists: products, users, messages, and more.
Arrays give you efficient ways to store, transform, and search that data.
const items = [value1, value2, value3]
items[index]
items.lengthconst fruits = ["apple", "banana", "mango"];
console.log(fruits[0]); // apple
console.log(fruits.length); // 3Arrays are zero-indexed and have a length property.
const list = [1, 2];
list.push(3);
list.pop();
console.log(list); // [1, 2]push and pop modify the array.
Arrays hold ordered collections of values. Indexes start at 0 and go up from there.
They are perfect for lists of items, records, or any sequence you need to process.
You can add, remove, and update items using push, pop, shift, and splice.
You can also create new arrays with map, filter, and slice.
Loop through arrays using for, for...of, or array methods like forEach.
Choose the style that is most readable for your use case.
Some methods mutate the original array (push, pop, splice, sort).
Others return new arrays (map, filter, slice). Know which behavior you need.
const nums = [1, 2, 3, 4];
const doubled = nums.map((n) => n * 2);
const evens = nums.filter((n) => n % 2 === 0);
console.log(doubled, evens);map and filter return new arrays.
const prices = [10, 20, 30];
const total = prices.reduce((sum, p) => sum + p, 0);
console.log(total);reduce collapses an array into a single value.
Without
const total = prices[0] + prices[1] + prices[2];With
const total = prices.reduce((sum, p) => sum + p, 0);Remember arrays start at index 0.
Use map, filter, or slice to create new arrays.
Prefer for...of or array methods for values.
Copy the array first if you need to preserve the original.
An ordered list of values accessed by index.
Use push, unshift, or spread to create a new array.
map, filter, and slice return new arrays.
Practice: Given an array of numbers, return a new array with only odd numbers.
const nums = [1, 2, 3, 4, 5];
// TODO: filter odd numbers
One Possible Solution
const nums = [1, 2, 3, 4, 5];
const odds = nums.filter((n) => n % 2 === 1);
console.log(odds);Yes, arrays are a special kind of object with indexed elements.
Performance is similar; choose the most readable approach.
Use slice() or spread: const copy = [...arr].
Try changing the array values and indexes.