JavaScript algorithms, math functions, etc.

prime-numbers.js

function isPrime(n) {
    // Eliminate any non-numeric values
    if (typeof(n) === 'boolean' || n === null || isNaN(n))
        return false;
    
    // Handle first two prime numbers 
    if (n === 2 || n === 3)
        return true;
    
    // Handle numbers that are definitely not prime
    if (n < 3 || n % 1 !== 0 || n % 2 === 0)
        return false;
    
    // Check if n divides evenly by any odd number between 3 and it's square root (inclusive)
    var divisor = 3; 
    while (divisor <= Math.sqrt(n)) {
        if (n % divisor === 0) return false;
        else divisor += 2;
    }
    
    // We can safely say that n is only evenly divisible by itself and 1, thus it is prime
    return true;
}