Arrays in JavaScript

What is an Array?

An array is a special variable that holds multiple values in an ordered list. You can store numbers, strings, objects, or even other arrays.

Creating Arrays

// Array literal (preferred)
let fruits = ["apple", "banana", "orange"];

// Using the Array constructor
let numbers = new Array(1, 2, 3, 4, 5);

// Empty array
let empty = [];

Accessing Array Elements

Use square brackets with the index (starting from 0).

let fruits = ["apple", "banana", "orange"];
console.log(fruits[0]); // "apple"
console.log(fruits[1]); // "banana"
console.log(fruits[2]); // "orange"
console.log(fruits.length); // 3

Common Array Methods

• push() — add an item to the end
• pop() — remove the last item
• unshift() — add an item to the beginning
• shift() — remove the first item
• includes() — check if an item exists
• indexOf() — find the index of an item
• slice() — create a copy of part of the array
• splice() — add or remove items at a specific index

Looping Through Arrays

let fruits = ["apple", "banana", "orange"];

// Traditional for loop
for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

// for...of loop (cleaner)
for (let fruit of fruits) {
  console.log(fruit);
}

Common Mistakes

• Off-by-one errors with array indices (arrays start at 0)
• Modifying arrays while iterating over them
• Using == to compare arrays (use === or compare elements)

Quick Quiz

Summary

• Arrays hold ordered lists of values
• Index starts at 0
• push() and pop() work with the end of the array
• unshift() and shift() work with the beginning
• includes() and indexOf() help find items
• slice() copies part of an array; splice() modifies it