Sieve of Eratosthenes in Javascript

Sieve_of_Eratosthenes.js

const numberNeeded = 20;
let isPrime = new Array(numberNeeded + 1).fill(true);

isPrime[0] = false; // setting 0 as not prime
isPrime[1] = false; // setting 1 as not prime
function sieve(n) {
  let j = 2;
  while (j * j <= n) {
    if (isPrime[j]) {
      for (let i = j * j; i <= n; i += j) {
        isPrime[i] = false;
      }
    }
    j++;
  }
}
sieve(numberNeeded);
console.log(isPrime);

// Output :
// [
// false, false, true,  true,
// false, true,  false, true,
// false, false, false, true,
// false, true,  false, false,
// false, true,  false, true,
// false
// ]