A simple demo of representing and using infinite sequences in JavaScript

InfiniteSequences.ts

import { iter } from 'iterator-helper';

/**
 * Represents a set of numbers from given start to a given end.
 * @param start The starting number in the range (default 0)
 * @param end The ending number in the range (default Infinity)
 */
const numbers = (start = 0, end = Infinity) =>
  iter(
    (function* () {
      let i = start;
      while (i < end) {
        yield ++i;
      }
    })()
  );

/**
 * Represents the set of all fibonacci numbers.
 */
const fib = () =>
  iter(
    (function* () {
      let [a, b] = [0, 1];
      while (true) {
        yield a;
        [a, b] = [b, a + b];
      }
    })()
  );

const add = (a: number, b: number) => a + b;
const double = (n: number) => n * 2;
const isEven = (n: number) => n % 2 === 0;

// Represents all even fibonacci numbers and double them.
const evenDoubleFib = fib().filter(isEven).map(double);

// Get the first 5 doubled and even primes
evenDoubleFib.take(5); // 0 4 16 68 288

/**
 * Detects if a number is prime or not.
 * @param num The number to check
 */
const isPrime = (num: number) => {
  for (let i = 2, s = Math.sqrt(num); i <= s; i++)
    if (num % i === 0) return false;
  return num > 1;
};

// Represents all prime numbers from the set of all natural numbers
const primes = () => numbers().filter(isPrime);

// Get the first 5 primes
primes().take(5); // 2 3 5 7 11

// Represents the sum of the first N prime numbers
const sumPrimes = (n: number) => primes().take(n).reduce(add, 0);

// Sum the first 5 prime numbers
sumPrimes(5); // 28

🥰

Insane