[Intermediate Algorithm Scripting: Sum All Primes | freeCodeCamp.org](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/sum-all-primes)

```js function primes(n) { / Validate input if (isNaN(n) || n < 1 || Math.floor(n) != n) { return 'The input number must be a positive integer, please enter a correct value' } if (n = 2) { return true } if (n % 2 = 0 || n = 1) { return false } / Check if number is prime for (let i = 3, limit = Math.sqrt(n); i <= limit; i += 2) { if (n % i = 0) { return false } } return true }

function sumPrimes(num) { let sum = 0 for (let i = 2; i <= num; i++) { if (primes(i)) { sum += i } } return sum }

console.log(sumPrimes(977)) / 2 3 5 7 / https://forum.freecodecamp.org/t/freecodecamp-challenge-guide-sum-all-primes/16085 // https://stackoverflow.com/a/12287599/12539782 ```

答案

```js function sumPrimes(num) { // Check all numbers for primality let primes = [] for (let i = 2; i <= num; i++) { if (primes.every((prime) > i % prime != 0)) primes.push(i) } return primes.reduce((sum, prime) => sum + prime, 0) } ```

```js function sumPrimes(num) { / Prime number sieve let isPrime = Array(num + 1).fill(true) / 0 and 1 are not prime isPrime[0] = false isPrime[1] = false for (let i = 2; i <= Math.sqrt(num); i++) { if (isPrime[i]) { // i has not been marked false – it is prime for (let j = i * i; j <= num; j += i) isPrime[j] = false } }

// Sum all values still marked prime return isPrime.reduce((sum, prime, index) => (prime ? sum + index : sum), 0) } ```