JavaScript Advanced Day 3: Advanced Arrays & Iterators

Goal of this Day

Today you will learn:

• How to handle arrays like a JavaScript ninja
• Advanced usage of map, filter, reduce
• Array methods: find, some, every
• Custom iterators and generators

By the end, you will manipulate complex data structures with ease.

Step 1: Advanced Array Methods

Using find, some, every:

const numbers = [1, 2, 3, 4, 5];

console.log(numbers.find(n => n > 3)); // 4
console.log(numbers.some(n => n > 4)); // true
console.log(numbers.every(n => n > 0)); // true

Step 2: Generators

Generators yield values lazily:

function* idGenerator() {
  let id = 1;
  while(true) yield id++;
}

const gen = idGenerator();
console.log(gen.next().value); // 1
console.log(gen.next().value); // 2

Step 3: Reduce for Deep Operations

Flatten nested arrays using reduce:

const nested = [[1,2], [3,4], [5]];
const flat = nested.reduce((acc, val) => acc.concat(val), []);
console.log(flat); // [1,2,3,4,5]

Practice

function* idGenerator() {
  let id = 1;
  while(true) yield id++;
}

const gen = idGenerator();
console.log(gen.next().value);
console.log(gen.next().value);

Task

Complete the following:

• Write a generator that yields even numbers
• Use .reduce() to flatten a nested array

Example:

// Generator for even numbers
function* evenNumbers() {
  let n = 2;
  while(true) yield n, n += 2;
}

const evGen = evenNumbers();
console.log(evGen.next().value); // 2
console.log(evGen.next().value); // 4

// Flatten nested array
const nested = [[1,2],[3,4],[5]];
const flat = nested.reduce((acc, val) => acc.concat(val), []);
console.log(flat); // [1,2,3,4,5]