beginner

JavaScript Arrays

Master JavaScript arrays for storing and manipulating collections of data.

Arrays are fundamental to JavaScript programming. They let you store multiple values in a single variable and provide powerful methods for adding, removing, and transforming data. From DOM element lists to API responses, arrays are used constantly in web development.

📚 Concepts & Theory

Creating Arrays:

const fruits = ["apple", "banana", "cherry"];
const numbers = [1, 2, 3, 4, 5];
const mixed = [1, "hello", true, null];

Accessing Elements:

console.log(fruits[0]);  // "apple"
console.log(fruits[fruits.length - 1]);  // "cherry" (last)

Common Array Methods:

// Adding elements
fruits.push("orange");     // Add to end
fruits.unshift("grape");   // Add to beginning

// Removing elements

fruits.pop();              // Remove from end

fruits.shift();            // Remove from beginning

// Finding elements

fruits.indexOf("banana");  // 1

fruits.includes("apple");  // true

Iterating Arrays:

fruits.forEach(fruit => {
    console.log(fruit);
});

const upperFruits = fruits.map(f => f.toUpperCase());

🎯 Your Challenge

Create an array called `colors` with "red", "green", "blue". Add "yellow" to the end using push(). Then find the index of "green" and store it in a variable called `greenIndex`.

📝 Starter Code

JavaScript

// Create the colors array
const colors = 

// Add "yellow" to the end


// Find the index of "green"
const greenIndex =

Arrays use square brackets []
push() adds to the end of an array
indexOf() returns the position of an element
Array indexes start at 0, not 1

Solution

JavaScript

const colors = ["red", "green", "blue"];

colors.push("yellow");

const greenIndex = colors.indexOf("green");

Explanation

We create the array with square brackets and string values. The push() method adds "yellow" to the end, making the array ["red", "green", "blue", "yellow"]. indexOf() returns 1 because "green" is at index 1 (arrays are zero-indexed).

⚠️ Common Mistakes to Avoid

Using add() instead of push()
Forgetting that arrays are zero-indexed
Using find() instead of indexOf() for position
Not including const when declaring the array

❓ Frequently Asked Questions

push() adds to the end of the array, while unshift() adds to the beginning. Similarly, pop() removes from the end and shift() removes from the beginning.

indexOf() returns -1 if the element is not in the array. You can use includes() for a boolean check instead.