gistfile1.js

// http://ejohn.org/apps/learn/#20
// caching results from a js function

function isPrime( num ) {
  var prime = num != 1; // Everything but 1 can be prime
  
  if (isPrime.cache[num]) {
    result = isPrime.cache[num];
  } else {
    for ( var i = 2; i < num; i++ ) {
      if ( num % i == 0 ) {
        prime = false;
        break;
      }
    }
    isPrime.cache[num] = prime;
    return prime;
  }
}
isPrime.cache = {};

assert( isPrime(5), "Make sure the function works, 5 is prime." );
assert( isPrime.cache[5], "Is the answer cached?" );