Kata

Implement a Least Recently Used (LRU) cache. An LRU cache is a key-value store that contains a set capacity for the number of elements it holds, which is stored in a property. The size should also be a property. When trying to add a new key-value pair, if cache.size == cache.capacity, the Least Recently Used key is removed.

Hint: You will will need to use the Object.defineProperty facility

Example Behavior:

var store = new LRUCache(3 // Size of the cache 
                        , {a: 1}); // Optional initial values for cache
store.size; // should be 1
store.capacity; // should be 3
store.a; // should be 1;
store.cache('b', 2)['b']; // should be 2
store.a = 5;
store.a; // should be 5
store.cache('c', 3).cache('d', 4).b; // should be undefined, since 'b' was removed because it was the least recently used
store.delete('d');
store.d ; // should be undefined, since 'd' was deleted
store.size ; // should be 2
store.cache('c', 4); 
store.c; // should be 4
store.capacity = 1; // should resize the store to have just one element
Object.keys(store); // should be ['c']

Full API Specification:

• The user should be able to make a new cache object with new LRUCache(n), where n is the cache's (initial) capacity
  • The constructor should be able to take a javascript object as an optional second parameter, which will be copied and put into the cache
• Items can be added to the cache using a method called cache
  • cache takes two arguments, a key and a value
    • The new key should be added as a property to the cache
    • The new property should be enumerable
    • It should be possible to reassign the new property
    • Caching an already existing property should update its value
  • The cache method should return the cache itself, so the method can be chained (ie, the builder pattern)
  • The cache method itself should not be enumerable, writable, nor configurable
• Items can be deleted from the cache using a method called delete
  • This method should not be enumerable, writable, nor configurable
  • This method should have the same return values as the delete builtin
• The number of elements stored in the cache should be accessible via the size property
  • This property should not be enumerable, writable nor configurable
• The capacity should be accessible by via the capacity property
  • Making the capacity smaller should trigger the cache to delete the least recently used items until the size of the cache is smaller than or equal to the capacity
  • This property should not be enumerable
  • The size property should never acceed the capacity property of a cache
• An item in the cache is used every time its value is read or assigned, or it is cached using the cache method