Simple Prime Sieve

primes.js

function getPrimes(howMany) {
    var primes = [], isPrime, primesCount = 0, candidate, primeIndex;
    
    for (candidate = 2; primesCount < howMany; candidate++) {
        for(primeIndex = 0, isPrime = true;
            primeIndex < primesCount && primes[primeIndex] <= Math.sqrt(candidate) && isPrime;) {

            isPrime = (candidate % primes[primeIndex++] === 0) ? false : true;
        }
        if(isPrime === false) {
            continue;
        }
        primes[primesCount++] = candidate;

    }
    return primes;
}