Finding the nth prime
A small function to compute the nth prime.
HTML
<script src="http://code.jquery.com/qunit/qunit-git.js"></script>
<link rel="stylesheet" href="http://code.jquery.com/qunit/qunit-git.css">
<div id="qunit"></div>
<div id="qunit-fixture"></div>
JavaScript
var prime = function (n) {
if (n > 100000) {
throw new Error("Not that many");
}
var primes = new Array(n + 1);
primes[1] = 2;
Find: for (var i = 2, test = 3; i <= n; test += 1) {
// see if test is prime and if so, it will be the ith prime.
for (var j = 1; j < i; j += 1) {
if (test % primes[j] === 0) {
continue Find;
}
}
primes[i] = test;
i += 1;
}
return primes[n];
};
QUnit.test("Primes test", function() {
equal(prime(1), 2);
equal(prime(2), 3);
equal(prime(3), 5);
equal(prime(4), 7);
equal(prime(5), 11);
equal(prime(6), 13);
equal(prime(10), 29);
equal(prime(100), 541);
//equal(prime(100000), 1299709);
});