primes.ts

export const {scan, isPrime, primes} = (() => {

    let primes: number[] = [2];
    let cursor = 2;
    const chunkSize = 100;
    const isPrimeAgainstKnown: (number: number) => boolean = number => primes.reduce((result, prime) => {
        return result && (number % prime !== 0)
    }, true)
    async function nextPrime(limit: number): Promise<number|null>{

        for (; cursor <= limit; cursor++) {
            if (isPrimeAgainstKnown(cursor)){
                primes.push(cursor);
                return cursor;
            }
        }
    }
    async function scanUntil(limit: number): Promise<void>{
        return new Promise((resolve, reject) => {
            async function scanChunk(){
                if (cursor >= limit){
                    return resolve();
                }
                const chunkLimit = Math.min(cursor + chunkSize, limit);
                const prime = await nextPrime(chunkLimit);
                setTimeout(scanChunk, 0)
            }
            scanChunk()
        });
    }
    
    async function scanUntil4(limit: number): Promise<void> {
        const timeout = 10; // 10ms -> ~650-700ms, 5ms -> 827ms (2..10000)

        return new Promise((resolve, reject) => {
            (async function loop() {
                const before = Date.now();
                while (cursor < limit && Date.now() - before < timeout){
                    await nextPrime(Math.min(cursor + chunkSize, limit));
                }
                if (cursor >= limit) {
                    return resolve();
                }
                nextTick(loop);
            })()
        });
    }

    const isPrime = async(number: number):Promise<boolean> => {
        if (number < 2 && number % 1 !== 0){
            return false;
        }
        await scanUntil4(number)
        return primes.includes(number)
    }

    return {
        scan,
        isPrime,
        primes: () => primes
    }
})();