Stuck on this challenge - Sum All Primes

JavaScript
1

I’ve been stuck on this too long. I’m trying to filter countList for all primes, but I’m not having any luck. I’m just having trouble finding the primes. I will write the condition that I want to pass:

  • The number is greater than 1 AND none of the divisors can divide the number without a remainder.
  function sumPrimes(num) {
  
  var countList = (function numberList(integer) {
    var array = [];
    
    for (var i = 2; i <= integer; i++) {
      array.push(i);
    }
    
    return array;
  }(num));
  
  return countList.filter(function(value) {
    for (var i = 1; i < value;) {
      return (value > 1) && (value % i === 0) ? value : false;
    }
  });
}            

sumPrimes(10);

Link to the challenge:

2

It looks like you have a good start with countList creating an array and pushing all the values from 2 up to and including num.

Let’s walkthrough what you’re trying to do with the filter method:

return countList.filter(function(value) { // filtering to return only the values that are true
    for (var i = 1; i < value;) { // looping through from 1 to the element to see if it is a prime. does the 'i' actually ever change if there is no third expression in the for loop in which to increment/decrement i?
      return (value > 1) && (value % i === 0) ? value : false; // this is saying return a true or false value right away to be in the new array or not
    }
  });

Things to think about:

  1. the for loop doesn’t have a third expression to increment i, so i will always be 1 and all the values in the array will be returned.
  2. is there a reason you need to start looping in the for loop with the number 1? any value modded by 1 will be 0 and that’s why the entire countList is returned.
  3. decide when to return true or false. might you return either true false while the loop is still continuing to the next i value in the for loop or maybe returning something when the loop is over or a combination of both?