Rediscovering JavaScript

Creating Infinite Iterators

Iterators in JavaScript are inherently lazy. They yield a value, wait for it to be consumed by the caller, and then, when requested for more, go on to produce the next value. While we can yield values from a known collection of data, we can also exploit this flexibility to create infinite sequences of data.

As an example, let’s create an infinite sequence of prime numbers. As a first step, we’ll define an isPrime() function that will tell us whether a given number is a prime number.

iterators/infinite-sequence.js

const isPrime = function(number) {
  for(let i = 2; i < number; i++) {
    if(number % i === 0) return false;
  }

  return number > 1;
};

The isPrime() function is a rather rudimentary implementation ...