stupid memoize

stupid-memoize.js

function memoize(fn) {
  var cache = {};
  
  // return a memoized version of the function
  return function(arg) {
    // intercept the argument
    if ( !(arg in cache) ) {
      // if it's not in cache, execute the original function and
      // cache the result, using the argument as the cache key.
      cache[arg] = fn.call(this, arg);
    }
    
    // now we're sure that the result is cached, so return it
    return cache[arg];
  };
}

usage.js

var nbExecutions = 0;
var square = function(n) {
  nbExecutions++;
  return n * n;
}
var squareMemoized = memoize(square);

squareMemoized(2); // === 4
// nbExecutions === 1
// cache is { '2': 4 }

squareMemoized(3); // === 9
// nbExecutions === 2
// cache is { '2': 4, '3': 9 }

// when the memoized function is executed with an argument that is already in
// the cache, the result is returned without executing the original function
squareMemoized(2); // === 4
// nbExecutions === 2
// cache is { '2': 4, '3': 9 }