Unrelated to passing the challenge - this solution has some serious efficiency concerns that will cause it to take a very long times as num gets big.
A few tips:
- Big arrays are slow. Only make arrays of information that you must have and cannot create otherwise.
- You don’t need to check if every number less that itself divides the number to know if the number is prime. (The largest possible factor of a number is it’s own square root)
Also, once you get a version that you think works quickly, it would be worth looking at the Sieve of Eratosthenes based approaches.
I did a bit of a write-up on performance of that approach here: JavaScript Performance Measurement & Variability