JSFiddle - React, Tailwind, and code Playground

by Axiniya

JavaScript

function primes(N) {
  let res = [2];
  for (let i = 3; i < N; i+=2) {
    let isPrime = true;
    for (let k = 0, limit = Math.sqrt(i); res[k] <= limit; ++k) {
      let d = res[k];
      if (i % d == 0) {isPrime = false;break;}
    }
    if (isPrime) res.push(i);
  }
  return res;
}

let res = primes(prompt('Введите число'));

console.log(res.length);