@alexander-nyberg/prime/index.js

find out if a number is prime or not

const primeTable = [
    2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,
    73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151,
    157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233,
    239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317,
    331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419,
    421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503,
    509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607,
    613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701,
    709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811,
    821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911,
    919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997,
];


function mightBePrime(maybeNumber)
{
    // this returns true if maybeNumber is a number, is positive, and is an
    // integer; and returns false otherwise.
    return typeof(maybeNumber) == 'number' && maybeNumber > 0 &&
        Math.floor(maybeNumber) == maybeNumber;
}

function primesInRange(begin, end)
{
    if (!mightBePrime(begin) || !mightBePrime(end)) {
        throw new TypeError("primesInRange expects two positive integers!");
    }
    
    else {
        var primes = [];
        
        // if end is within the bounds if primeTable, simply check if i is in
        // the primeTable.
        if (end <= 1000) {
            for (var i = begin; i < end; i++) {
                if (primeTable.includes(i)) {
                    primes.push(i);
                }
            }
        }
        
        // otherwise, go up to 1000 using the primeTable, and then use the
        // primes created to go up to the desired range.
        else {
            for (var i = begin; i <= 1000; i++) {
                if (primeTable.includes(i)) {
                    primes.push(i);
                }
            }
            
            var primeOrNot = true;
            
            for (var i = 1001; i < end; i++) {
                primeOrNot = true;
                
                for (prime of primes) {
                    if (i % prime == 0) {
                        primeOrNot = false;
                        break;
                    }
                }
                
                if (primeOrNot) {
                    primes.push(i);
                }
            }
        }
        
        return primes;
    }
}

function isPrime(number)
{
    if (!mightBePrime(number)) {
        throw new TypeError("isPrime expects a positive integer!");
    }
    
    // if number is in the range [1,1000], return whether it is in primeTable.
    else if (number <= 1000) {
        return primeTable.includes(number);
    }
    
    // else generate the primes up to and including number and check if it is
    // in the resulting array.
    else {
        return primesInRange(1, number + 1).includes(number);
    }
}

function isNotPrime(number)
{
    if (!mightBePrime(number)) {
        throw new TypeError("isNotPrime expects a positive integer!");
    }
    
    else {
        return !isPrime(number);
    }
}


module.exports = {
    mightBePrime: mightBePrime,
    primesInRange: primesInRange,
    isPrime: isPrime,
    isNotPrime: isNotPrime,
};

//for (var i = 1; i < 10000; i++) {
//    if (isPrime(i)) { console.log(i); }
//}