JS Arrays

JS Arrays

Arrays store multiple values in a single variable. They are ordered and zero-indexed.

const fruits = ["Apple", "Banana", "Orange"];

console.log(fruits[0]);
console.log(fruits.length);

Arrays can hold mixed data types.

const mixed = [1, "text", true, { name: "Ozan" }];

JS Array Methods

Common methods for modifying arrays:

const numbers = [1, 2, 3];

numbers.push(4);    // add to end
numbers.pop();      // remove last
numbers.shift();    // remove first
numbers.unshift(0); // add to start

console.log(numbers);

Non-mutating methods:

const arr = [1, 2, 3, 4];

console.log(arr.slice(1, 3));  // [2,3]
console.log(arr.concat([5,6]));

JS Array Search

Search inside arrays using built-in methods.

const items = ["a", "b", "c", "b"];

console.log(items.indexOf("b"));
console.log(items.lastIndexOf("b"));
console.log(items.includes("c"));

Modern search methods:

const users = [
  { id: 1, name: "Ali" },
  { id: 2, name: "Veli" }
];

console.log(users.find(u => u.id === 2));
console.log(users.findIndex(u => u.name === "Ali"));

JS Array Sort

By default, sort() converts values to strings.

const nums = [10, 5, 100];

nums.sort();
console.log(nums); // wrong numeric sort

Use a compare function for numeric sorting.

nums.sort((a, b) => a - b);
console.log(nums);

Modern immutable alternatives:

const sorted = nums.toSorted((a, b) => a - b);
console.log(sorted);

JS Array Iterations

Iteration methods are powerful and commonly used.

const values = [1, 2, 3, 4];

values.forEach(v => console.log(v));

const doubled = values.map(v => v * 2);
const filtered = values.filter(v => v > 2);
const total = values.reduce((sum, v) => sum + v, 0);

console.log(doubled, filtered, total);

Flatten nested arrays:

const nested = [1, [2, 3], [4]];
console.log(nested.flat());

JS Array Const

Arrays declared with const cannot be reassigned, but their contents can change.

const arr2 = [1, 2, 3];

arr2.push(4); // allowed
// arr2 = [5,6]; // Error

console.log(arr2);

Modern Patterns

Spread operator:

const a = [1,2];
const b = [...a, 3, 4];
console.log(b);

Destructuring:

const list = [10, 20, 30];
const [first, second] = list;

console.log(first, second);

Array.isArray check:

console.log(Array.isArray(list));

JS Array Reference

Arrays include many methods such as push, pop, map, filter, reduce, find, sort, flat, and more.

Next Step

Continue with JS Sets to learn how to store unique values.