primes-opt.js

// Naive prime calculator
function isPrime(x) {
    for (i = 2; i < x; i++) {
        if (x % i == 0) {
            return false
        }
    }
    return true
}

function findPrime(i) {
    prime = i;
    do {
        prime = prime + 1;
        if (isPrime(prime)) {
            return prime;
        }
    } while (true);
}

// Prime number calculator based on the Sieve of Eratosthenes algorithm.
class AcceptFilter {
    accept(n) {
        return true
    }
}

class DivisibleByFilter {
    constructor(number, next) {
        this.number = number;
        this.next = next;
    }

    accept(n) {
        var filter = this;
        // if (filter != null) {
        while (filter != null) {
            if (n % filter.number === 0) {
                return false;
            }
            // return filter.next.accept(n);
            filter = filter.next;
        }
        return true;
    }
}

class Primes {
    constructor() {
        this.number = 2;
        this.filter = new AcceptFilter();
    }

    next() {
        while (!this.filter.accept(this.number)) {
            this.number++;
        }
        this.filter = new DivisibleByFilter(this.number, this.filter);
        return this.number;
    }
}

// Verify results are the same
var primes = new Primes();
var lastPrime = 1;
for (let i = 1; i <= 1000; i++) {
    sievePrive = primes.next()
    naivePrime = findPrime(lastPrime)
    lastPrime = naivePrime
    if (naivePrime != sievePrive || !isPrime(sievePrive)) {
        throw "Error!" + i
    }
}
console.log('OK')