Check if a given integer is a prime number

Trial division up to the square root, without allocating an array.

JavaScript Version 1.0.0 · MIT · .md

function isPrime(n) { if (n < 2) return false; for (let i = 2; i * i <= n; i++) if (n % i === 0) return false; return true; }

Input & expected output

97

true

The edge case

1

false

Know the limits

• The original built an array of candidates; a loop stops at the first divisor and allocates nothing.
• Fine for numbers up to the lab’s one billion; use a sieve for many queries.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Check whether all values are equal — Compare every item with the first using Object.is.
• Check whether an object is empty — Check for own enumerable string keys on a JSON object.
• Check whether an integer is even — Test parity for safe integers, including zero and negative values.