30-seconds-of-code
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A collection of useful JavaScript snippets.
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Markdown
Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from `2` to the given number. Use `Array.filter()` to filter out the values divisible by any number from `2` to the square root of the provided number.
```js
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;
};
```
```js
primes(10); // [2,3,5,7]
```