JavaScript Intermediate Day 2: Arrays Advanced

Goal of this Day

Today you will learn:

• How to work like a pro with arrays
• Using .map() to transform arrays
• Using .filter() to select elements
• Using .reduce() to combine array values

By the end, you will be able to manipulate arrays efficiently in JavaScript.

Step 1: map()

map() creates a new array by transforming each element.

let numbers = [1, 2, 3, 4];

let doubled = numbers.map(n => n * 2);
console.log(doubled); // [2, 4, 6, 8]

Step 2: filter()

filter() selects elements based on a condition.

let numbers = [1, 2, 3, 4];

let evens = numbers.filter(n => n % 2 === 0);
console.log(evens); // [2, 4]

Step 3: reduce()

reduce() combines all elements into a single value.

let numbers = [1, 2, 3, 4];

let sum = numbers.reduce((total, n) => total + n, 0);
console.log(sum); // 10

Practice

let numbers = [1, 2, 3, 4];

let doubled = numbers.map(n => n * 2);
console.log(doubled);

Task

Complete the following tasks:

• Filter numbers > 10 from an array
• Sum all numbers using reduce()

Example:

let numbers = [5, 12, 8, 20];

let filtered = numbers.filter(n => n > 10);
console.log(filtered); // [12, 20]

let total = numbers.reduce((sum, n) => sum + n, 0);
console.log(total); // 45