// Mei Weng Brough-Smyth

// beepboop.com.au

​

var limit;

​

// Take input and ensure it is an integer.

function validInteger(){

  document.getElementById("junk").innerHTML = "";

  var input = document.getElementById('input').value;

  limit = input.match(/^\d+$/);

  limit++; // Add 1 to compensate for place 0

  doSieve(limit);

}

​

// Take limit and output using sieve of eratosthenes

function doSieve(limit) {

  // Create array with limit amount of elements

  var sieve= new Array(limit);

  // set 1 and 2 to false

  sieve[0] = false;

  sieve[1] = false;

  // Set elements that divide equally by 2 to false and the rest to true

  for (var i=2; i<limit; i++) {

      i%2===0 ? sieve[i] = false : sieve[i] = true;

    }

  // Get square root of limit

  var squareLimit = Math.sqrt(limit);

​

  // Get all primes from 2 to the square limit

  for (i=2; i<squareLimit; i++) {

    if (sieve[i]) {

      // Get all multiples of these primes and set them to false

      for (var j=i*2; j<=limit; j+=i) {

        sieve[j] = false;

      }

    }

  }

  // Print out prime result

  for (i=1; i<limit; i++) {

    if (sieve[i]) {

      document.getElementById("junk").innerHTML += i + ", ";

    }

  }

}