Javascript Prime Numbers

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Source code

  <script type="text/javascript">
//<![CDATA[
    // calculate successive prime numbers
    var Prime = function() {
      // current prime number
      this.prime = 1;

      // return true if NUM is prime
      this.isPrime = function(num) {
        var result = true;
        if (num !== 2) {
          if (num % 2 == 0) {
            result = false;
          } else {
            for (x=3; x<=Math.sqrt(num); x+=2) {
              if (num % x == 0) result = false;
            }
          }
        }
        return result;
      }

      // return next prime number
      this.nextPrime = function() {
        this.prime++;
        while (!this.isPrime(this.prime)) this.prime++;
        return this.prime;
      }
    }

    // prime
    this.prime = new Prime();

    // current delay
    this.delay = 100;

    // calculate primes
    function calcPrimesLoop() {
      var primes = document.getElementById('primes');
      primes.appendChild(document.createTextNode(' '+this.prime.nextPrime()));
      calcPrimesDelay = setTimeout('calcPrimesLoop()', this.delay);
    }

    // start calculating primes
    function calcPrimesStart() {
      var prime = this.prime.nextPrime();
      var calculate = document.getElementById('calculate');
      calculate.href = 'javascript:calcPrimesStop()';
      calculate.firstChild.data = 'calculate on';
      var primes = document.getElementById('primes');
      var spacer = ' ';
      if (prime == 2) spacer = '';
      primes.appendChild(document.createTextNode(spacer+prime));
      scrollPrimesStart();
      calcPrimesDelay = setTimeout('calcPrimesLoop()', this.delay);
    }

    // stop calculating primes
    function calcPrimesStop() {
      clearTimeout(calcPrimesDelay);
      var calculate = document.getElementById('calculate');
      calculate.href = 'javascript:calcPrimesStart()';
      calculate.firstChild.data = 'calculate off';
      scrollPrimesStop();
    }

    // scroll primes text area
    function scrollPrimesLoop() {
      var primes = document.getElementById('primes');
      primes.scrollTop = primes.scrollHeight;
      scrollDelay = setTimeout('scrollPrimesLoop()', 100);
    }

    // start scrolling primes text area
    function scrollPrimesStart() {
      var scroll = document.getElementById('scroll');
      scroll.href = 'javascript:scrollPrimesStop()';
      scroll.firstChild.data = 'scrolling on';
      scrollPrimesLoop();
    }

    // stop scrolling primes text area
    function scrollPrimesStop() {
      clearTimeout(scrollDelay);
      var scroll = document.getElementById('scroll');
      scroll.href = 'javascript:scrollPrimesStart()';
      scroll.firstChild.data = 'scrolling off';
    }

    // set delay
    function setDelay(delay) {
      this.delay = delay;
    }

    window.onload = calcPrimesStart;
//]]>
    </script>

    <textarea id="primes" rows="20"></textarea>

    &nbsp;&nbsp;
    <a id="calculate">calculate on</a>
    &nbsp;&nbsp;
    <a id="scroll">scrolling on</a>
    &nbsp;&nbsp;
    <a id="slowSpeed" href="javascript:setDelay(1000)">slow</a>
    &nbsp;&nbsp;
    <a id="normalSpeed" href="javascript:setDelay(100)">normal</a>
    &nbsp;&nbsp;
    <a id="fastSpeed" href="javascript:setDelay(0)">fast</a>