Prime Number

prime.js

function Prime() {
    this.prime = 1;
}

Prime.prototype.isPrime = function(num) {
    var result = true, maxToCheck = Math.ceil(Math.sqrt(num)); // integer number comparison is faster

    if (num & 1) { // if odd number
        for (var f = 3; f <= maxToCheck; f += 2) {
            if (!(result = !!(num % f))) return false;
        }
    } else { // if even
        return num === 2;
    }
    
    return result;
}

Prime.prototype.getNextPrime = function() {
    // a prime number is not even, save one iteration for ++
    while (!this.isPrime(++this.prime));
    return this.prime;
}