gre/index.html

## index.html
<!DOCTYPE html>
<html>
  <head>
    <script type="text/javascript" src="jquery-1.4.2.min.js"></script>
    <style>
      body {
          color: #333;
          background: #EEE;
          margin: 30px;
      }
      h1 {
        padding-left: 40px;
      }
      .number {
          font-family: monospace;
          font-size: 0.9em;
          color: white;
          background: #666;
          min-width: 50px;
          min-height: 50px;
          padding: 5px;
      }
      .number.searching {
          background: #44C;
      }
      .number.prime {
          background: #4C4;
      }
      .number.notPrime {
          background: #C44;
      }
    </style>

    <script type="text/javascript">
    $(function(){

	var MAX_NUMBER = 99;
	var randomNumber = function() {
            return Math.ceil(Math.random()*MAX_NUMBER);
	};

	var newNumbers = function(){
            $('#numbers .number').each(function(){
		var number = randomNumber();
		var numberNode = $(this);
		numberNode.text(number).attr('class', 'number searching');
		var worker = new Worker("primeSolver.js");

		worker.onmessage = function(message) {
		  worker.terminate();
		  var isPrime = message.data;
		  numberNode.removeClass('searching').addClass(isPrime ? 'prime' : 'notPrime');
		}

		worker.postMessage(number);
            })
	}

	$('#randomizeNumbers').click(newNumbers);
    });
    </script>
  </head>

  <body>

    <p>
      <button id="randomizeNumbers">Randomize numbers</button>
    </p>

    <table id="numbers">
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
      <tr>
        <td class="number">
        <td class="number">
        <td class="number">
      </tr>
    </table>
  </body>
</html>

## primeSolver.js

function findPrimeFactors(number) {
  var newNumber = number;
  var factors = [];
  var checker = 2;
  while (checker*checker <= newNumber) {
    if (newNumber % checker == 0) {
      factors.push(checker);
      newNumber /= checker;
    }
    else
      checker++;
  }
  if (newNumber != 1)
    factors.push(newNumber);
  return factors;
}
function isPrime(number) {
  return (findPrimeFactors(number).length == 1);
}

onmessage = function(message) {
  var number = message.data;
  var prime = isPrime(number);
  postMessage(prime);
}
	<!DOCTYPE html>
	<html>
	<head>
	<script type="text/javascript" src="jquery-1.4.2.min.js"></script>
	<style>
	body {
	color: #333;
	background: #EEE;
	margin: 30px;
	}
	h1 {
	padding-left: 40px;
	}
	.number {
	font-family: monospace;
	font-size: 0.9em;
	color: white;
	background: #666;
	min-width: 50px;
	min-height: 50px;
	padding: 5px;
	}
	.number.searching {
	background: #44C;
	}
	.number.prime {
	background: #4C4;
	}
	.number.notPrime {
	background: #C44;
	}
	</style>

	<script type="text/javascript">
	$(function(){

	var MAX_NUMBER = 99;
	var randomNumber = function() {
	return Math.ceil(Math.random()*MAX_NUMBER);
	};

	var newNumbers = function(){
	$('#numbers .number').each(function(){
	var number = randomNumber();
	var numberNode = $(this);
	numberNode.text(number).attr('class', 'number searching');
	var worker = new Worker("primeSolver.js");

	worker.onmessage = function(message) {
	worker.terminate();
	var isPrime = message.data;
	numberNode.removeClass('searching').addClass(isPrime ? 'prime' : 'notPrime');
	}

	worker.postMessage(number);
	})
	}

	$('#randomizeNumbers').click(newNumbers);
	});
	</script>
	</head>

	<body>

	<p>
	<button id="randomizeNumbers">Randomize numbers</button>
	</p>

	<table id="numbers">
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	<tr>
	<td class="number">
	<td class="number">
	<td class="number">
	</tr>
	</table>
	</body>
	</html>

	function findPrimeFactors(number) {
	var newNumber = number;
	var factors = [];
	var checker = 2;
	while (checker*checker <= newNumber) {
	if (newNumber % checker == 0) {
	factors.push(checker);
	newNumber /= checker;
	}
	else
	checker++;
	}
	if (newNumber != 1)
	factors.push(newNumber);
	return factors;
	}
	function isPrime(number) {
	return (findPrimeFactors(number).length == 1);
	}

	onmessage = function(message) {
	var number = message.data;
	var prime = isPrime(number);
	postMessage(prime);
	}