Simple trial division in JavaScript

Question

I began programming recently. I am trying to implement a simple trial-division algorithm for finding all primes up to some number (it is much more "primitive" algorithm than the Sieve of Eratosthenes). Can you please find what's wrong with my code?

#range function:

range = function (a,b,c){
    var range1=[]
    for (i=a; i<b; i=i+c){
        range1.push(i);
    }
    return range1;
}

#The algorithm:

n=prompt("n");
var numbers=range(2,n,1);
var primes=[];
for (number in numbers){
 var sublist=range(2,number,1);
 console.log(sublist);
 for (x in sublist){
  if (number%x ===0){
   break;
  }
 primes.push(number); 
 }
}

Thanks in advance!

Answer 1

Try using this instead.

// `isPrime` adopted from http://www.javascripter.net/faq/numberisprime.htm
var isPrime = function (n) {
    if (isNaN(n) || !isFinite(n) || n % 1 || n < 2) {
        return false;
    }
    if (n % 2 === 0){
        return (n === 2);
    }
    if (n % 3 === 0){
        return (n === 3);
    }
    for (var i = 5, m = Math.sqrt(n); i <= m; i += 6) {
        if ((n % i === 0) || (n % (i + 2) === 0)){
            return false;
        }
    }
    return true;
}
var getPrimesUntilN = function (n) {
    n = Math.abs(n);
    var primes = (1 < n) ? [2] : [];
    if (isNaN(n) || !isFinite(n)) {
        return primes;
    }
    for (var i = 3; i <= n; i+=2) {
        if (isPrime(i)) {
            primes.push(i);
        }
    }
    return primes;
};

Input:

getPrimesUntilN(50);

Output:

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

Answer 2

range = function (a,b,c){
    var range1=[]
    for (i=a; i<b; i=i+c){
        range1.push(i);
    }
    return range1;
}

//#The algorithm:

n=prompt("n");
var numbers=range(2,n,1);

var primes=[];
for (y=0; y<numbers.length;y++)
{
  var sublist=range(2,numbers[y],1), isPrime = true;

  for (x=0; x<sublist.length;x++)
  {
   if (numbers[y] % sublist[x] === 0)
   {
     isPrime = false;
     break;
   }
 }
 if(isPrime)
 {
     primes.push(numbers[y]); 
 }
}
console.log(primes);