Sieve of Eratosthenes

sieve_of_eratosthenes.js

/*jshint esnext: true */

/*
https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
1. Create a list of consecutive integers from 2 through n: (2, 3, 4, ..., n).

2. Initially, let p equal 2, the smallest prime number.

3. Enumerate the multiples of p by counting to n from 2p in increments of p, and mark them in the list (these will be 2p, 3p, 4p, ...; the p itself should not be marked).

4. Find the first number greater than p in the list that is not marked. If there was no such number, stop. Otherwise, let p now equal this new number (which is the next prime), and repeat from step 3.

5. When the algorithm terminates, the numbers remaining not marked in the list are all the primes below n.

*/

function*  numberMaker(max) {
  var index = 1;
  while(index<=max)
    yield index++;
}

function sieve(max){
  let numbers = [... numberMaker(max)];
  let marked = [];
  let primes = [];

  let p=2;

  while (p<max) {
    for (n=p; n<=max; n=n+p) {
      if (marked.indexOf(n)<0 && n!==p){
        //mark the number if it's not marked and not p
        marked.push(n);
      }
    }
    //make p the next highest unmarked number
    p = numbers.find(number=> (number > p && marked.indexOf(number)<0));
  }
  //get all the numbers which are not marked
  primes = numbers.filter(number => marked.indexOf(number)<0)
  return primes;
}

console.log(sieve(2000));