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Javascript prime number generator
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<!DOCTYPE html> | |
<html> | |
<head> | |
<title>JS Prime Generator</title> | |
</head> | |
<body> | |
<div id="res"></div> | |
<button id="generate">Generate more primes!</button> | |
<script type="text/javascript"> | |
(function(){ | |
"use strict"; | |
//Add event listener to the button | |
document.getElementById("generate").addEventListener("click", get_primes, false); | |
var timeDiff = { | |
setStartTime:function () | |
{ | |
var d = new Date(); | |
this.time = d.getTime(); | |
}, | |
getDiff:function () | |
{ | |
var d2 = new Date(); | |
return (d2.getTime()-this.time); | |
} | |
}; | |
function get_primes() | |
{ | |
//Start the timer | |
timeDiff.setStartTime(); | |
//Define primes array | |
var primes = []; | |
//Check for "primes" key in localstorage | |
if(localStorage.getItem("primes") != null) | |
{ | |
var existing_primes = JSON.parse(localStorage.getItem("primes")); | |
var num_primes = existing_primes.length; | |
// If there is a "primes" key in localstorage, add it to the | |
// primes array | |
for(var i=0;i< num_primes;i++) | |
{ | |
primes.push(existing_primes[i]); | |
} | |
} | |
else //Seed the prime generator with the first prime number | |
{ | |
primes.push(2); | |
} | |
// Get the largest existing prime, and add one | |
// to make it the starting number in the search for the next prime | |
var start_num = primes[primes.length - 1] + 1; | |
// Specify a sane ending point | |
var end_num = 999 + start_num; | |
// Speed it up a tad | |
if(start_num % 2 === 0) | |
{ | |
start_num++; | |
end_num++; | |
} | |
// Flag for determining if a number is prime | |
var is_prime = true; | |
var x = 0; | |
for(i = start_num;i < end_num;i+=2) | |
{ | |
is_prime = true; | |
num_primes = primes.length; | |
for(x=0;x<num_primes;x++) | |
{ | |
//If the remainder is 0, the number is a composite | |
if(i % primes[x] === 0) | |
{ | |
is_prime = false; | |
break; | |
} | |
} | |
// If the number is prime, add it to the primes array | |
if(is_prime === true) | |
{ | |
primes.push(i); | |
} | |
} | |
//Save the array in localStorage for the next round(s) | |
localStorage.setItem("primes", JSON.stringify(primes)); | |
var output = ""; | |
//String together all the primes | |
output += primes.join(", "); | |
output += '<br /><br />'; | |
var total_time = timeDiff.getDiff(); | |
output += 'Generated '+primes.length+' primes in '+(total_time / 1000)+' seconds.'; | |
document.getElementById('res').innerHTML = output; | |
location.href="#generate"; | |
} | |
}()); | |
</script> | |
<button onclick="localStorage.setItem('primes', '[2]')">Start Over</button> | |
</body> | |
</html> |
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