How to find prime numbers between 0 - 100?

Answer 1

A number is a prime if it is not divisible by other primes lower than the number in question.

So this builds up a primes array. Tests each new odd candidate n for division against existing found primes lower than n. As an optimization it does not consider even numbers and prepends 2 as a final step.

var primes = [];
for(var n=3;n<=100;n+=2) {
  if(primes.every(function(prime){return n%prime!=0})) {
    primes.push(n);
  }
}
primes.unshift(2);