# Primes up to given number

JavaScript, Math, Algorithm · Dec 28, 2020

Generates primes up to a given number, using the Sieve of Eratosthenes.

• Generate an array from `2` to the given number.
• Use `Array.prototype.filter()` to filter out the values divisible by any number from `2` to the square root of the provided number.
```const primes = num => {
let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
sqroot = Math.floor(Math.sqrt(num)),
numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y === x)));
return arr;
};```
`primes(10); // [2, 3, 5, 7]`

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