PrimeNumberGenerator.js

function PrimeNumberGenerator() {
    this.indx = 2;
}

PrimeNumberGenerator.prototype.next = function () {
    var counter = 2;

    while (counter < this.indx) {
        if (this.indx % counter++ === 0) {
            counter = 2;
            this.indx++;
        }
    }

    return this.indx++;
}

var myPrimes = new PrimeNumberGenerator();

myPrimes.next(); // 2
myPrimes.next(); // 3
myPrimes.next(); // 5
myPrimes.next(); // 7
myPrimes.next(); // 11
myPrimes.next(); // 13
// ...