Intro to Array

An array is an ordered list. It lets you store multiple values in a single variable and access them by position.

Creating an Array

Use square brackets:

const colors = ["red", "green", "blue"];
const numbers = [1, 2, 3, 4, 5];
const mixed = ["hello", 42, true, null];

Arrays can hold any type of value, including other arrays.

Accessing Items by Index

Items are numbered starting at zero:

const fruits = ["apple", "banana", "cherry"];

fruits[0]; // 'apple'
fruits[1]; // 'banana'
fruits[2]; // 'cherry'
fruits[3]; // undefined — past the end

The last item is always at index array.length - 1.

Checking Length

fruits.length; // 3

Modifying Values

You can update an item directly by index:

fruits[1] = "mango";
// ['apple', 'mango', 'cherry']

Arrays Are Reference Types

When you assign an array to a variable, both variables point to the same array:

const a = [1, 2, 3];
const b = a;
b.push(4);
console.log(a); // [1, 2, 3, 4] — a changed too

If you want an independent copy, use slice() or the spread operator:

const b = [...a]; // independent copy

Next Steps

Once you’re comfortable with arrays, the real power comes from array methods: forEach, map, filter, find, and reduce. Each one solves a specific kind of problem without writing a loop manually.