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Harnessing the Power of Iterators and Generators for Custom Iteration Control in JavaScript

Alka Vats
Alka Vats
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JavaScript’s Iterators and Generators are powerful features that allow developers to create custom iteration control over data structures. These constructs enable you to define your own iteration logic. It is easier to work with collections, perform asynchronous operations, and handle infinite sequences. So, In this blog, we’ll delve into Iterators and Generators, and their advantages, and provide practical examples of their usage.

If you want to learn about the comparison between typescript and javascript, you can refer here.

Understanding Iterators:

An Iterator is an object that provides a sequence of values or elements from a data structure, one at a time. It follows a standard interface with two primary methods:

  1. next(): This method returns an object with two properties: value (the current value in the iteration) and done (a boolean indicating whether the iteration has reached its end).
  2. Symbol.iterator: This symbol is a key used to define the iterator for an object. When an object implements this symbol, it becomes iterable, allowing you to use the for...of loop or other iterable-related features in JavaScript.

Advantages of Iterators:

  • Custom Iteration Control: With Iterators, you can implement your own logic for iterating over data structures, enabling you to traverse objects in unique ways.
  • Lazy Evaluation: Iterators use lazy evaluation, meaning they only generate values when requested, which can be highly beneficial when dealing with large datasets.
  • Reusability: Once you implement an Iterator for a specific data structure, it can be reused across various parts of your codebase, promoting code modularity.

Understanding Generators:

Generators are special functions in JavaScript denoted by an asterisk (function*). They allow you to define an iterator’s behavior using a concise and readable syntax. Unlike regular functions, Generators can pause and resume their execution, making them ideal for handling asynchronous operations and infinite sequences.

Therefore, to pause the execution of a Generator and return a value, you use the yield keyword. So, When the Generator is resumed, it picks up where it left off, maintaining its context.

Advantages of Generators:

  • Asynchronous Operations:
    Generators simplify the handling of asynchronous tasks by making it easier to write asynchronous code in a synchronous style. It enhances code readability and maintainability.
  • Infinite Sequences:
    Generators can produce an infinite sequence of values, useful for scenarios like generating Fibonacci series, prime numbers, and more.

Example: Using Iterators and Generators

Let’s illustrate the concepts of Iterators and Generators with a practical example of creating a custom range iterator and an infinite sequence generator for prime numbers.

Custom Range Iterator
function rangeIterator(start, end) {
  let current = start;
  return {
    next() {
      if (current <= end) {
        return { value: current++, done: false };
      } else {
        return { done: true };
    [Symbol.iterator]: function () {
      return this;

const myRange = rangeIterator(1, 5);
for (const num of myRange) {
Infinite Sequence Generator for Prime Numbers
function* primeNumberGenerator() {
  let num = 2;
  while (true) {
    if (isPrime(num)) {
      yield num;

function isPrime(num) {
  if (num <= 1) return false;
  for (let i = 2; i <= Math.sqrt(num); i++) {
    if (num % i === 0) return false;
  return true;

const primeGen = primeNumberGenerator();
for (let i = 0; i < 5; i++) {


Iterators and Generators are versatile features in JavaScript. It allows you to take control of data structure iteration and streamline the handling of asynchronous operations. By implementing custom iterators, you can make your code more modular and reusable, while generators enable you to deal with infinite sequences and asynchronous tasks in a more elegant and readable manner. Understanding these concepts opens up a new realm of possibilities for your JavaScript projects, making them more efficient and easier to maintain.

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Alka Vats

Alka Vats

Alka Vats is a Software Consultant at Nashtech. She is passionate about web development. She is recognized as a good team player, a dedicated and responsible professional, and a technology enthusiast. She is a quick learner & curious to learn new technologies. Her hobbies include reading books, watching movies, and traveling.

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