Nested map

nested-map.js

// a memoizer that works with functions that receive two arguments
// of any type (can be generalized to accept more arguments)
function memoize(fn) {
  // The first level of our nested-cache
  var cacheLevel1 = new Map();

  return function(arg1, arg2) {
    // Let's check the cache, using one argument at each level
    if ( !cacheLevel1.has(arg1) ) {
      // and create nested maps as we need them
      const cacheLevel2 = new Map();
      cacheLevel2.set(arg2, fn.call( this, arg1, arg2 ));
      cacheLevel1.set(arg1, cacheLevel2);

    } else if ( !cacheLevel1.get(arg1).has(arg2) ) {
      cache.get(arg1).set(arg2, fn.call( this, arg1, arg2 ));
    }

    return cache.get(arg1).get(arg2);
  };
}