memoize.js

/*
  This piece has been taken from React.js Conf 2015 - Immutable Data and React
*/
function memoize(fn) {
  var prevArg;
  var prevResult;
  return function(arg) {
    return arg === prevArg ?
      prevResult : 
      (prevArg = arg, 
       prevResult = fn.call(this, arg));
  }
}