primality-regex.js

/**
 * Adapted from <http://neilk.net/blog/2000/06/01/abigails-regex-to-test-for-prime-numbers/>.
 */
function isPrime(n) {
    return !/^#?$|^(##+?)\1+$/.test(Array(n+1).join('#'));
}
 
(function (n){return !/^#?$|^(##+?)\1+$/.test(Array(n+1).join('#'))})(1); // false
(function (n){return !/^#?$|^(##+?)\1+$/.test(Array(n+1).join('#'))})(2); // true
(function (n){return !/^#?$|^(##+?)\1+$/.test(Array(n+1).join('#'))})(7); // true
(function (n){return !/^#?$|^(##+?)\1+$/.test(Array(n+1).join('#'))})(9); // false