LRU Cache Implementation

lru.js

/**
 * LRU Cache
 *
 * http://www.codewars.com/kata/53b406e67040e51e17000c0a
 * 
 */
function LRUCache(capacity, init) {
  var data = init || {};
  var timestamps = {};
  var capacity = capacity;
  
  var getTimestamp = function() {
    var time = Date.now();
    
    while(time === Date.now());
    return Date.now();
  };
  
  var findLRU = function() {
    var keys = Object.keys(timestamps);
   
    return keys
      .reduce(function(acc, x) { 
        if (timestamps[x] < acc.time) { 
          return {key: x, time: timestamps[x]} ; 
        } else { return acc;} 
    }, {key: keys[0], time: timestamps[keys[0]] });
  };

  var cache = function(key, val) {
    if (!key) return data;
    if (key && val) {
      setCache(key, val); 
    }
    
    if (this.size > this.capacity) {
      var lruItem = findLRU();
      deleteCache(lruItem.key);
    }
        
    return this;
  }.bind(this);
  
  var setCache = function(key, value) {
    if (!this[key]) {
      Object.defineProperty(this, key, {
        get: function() { return data[key]; },
        set: function(value) { data[key] = value; timestamps[key] = getTimestamp(); },
        enumerable: true,
        configurable: true
      });
    }
    
    this[key] = value;
    
  }.bind(this);
  
  var deleteCache = function(key) {
      if (typeof this[key] === 'function' || key === 'capacity' || key === 'size') {
        return false;
      }
      
      if (typeof data[key] !== 'undefined' && data[key]) {
        delete data[key];
        delete this[key];
      }
      
      if (typeof timestamps[key] !== 'undefined') {
        delete timestamps[key];
      }
      
      return true;
  }.bind(this);
  
  Object.defineProperty(this, 'size', {
    get: function() {
      return Object.keys(data).length;
    }
  });
  
  Object.defineProperty(this, 'cache', { 
    value: cache,
    enumerable: false,
    writable: false,
    configurable: false
  });
  
  Object.defineProperty(this, 'delete', {
    value: function(key) { return deleteCache(key); },
    enumerable: false,
    writable: false,
    configurable: false
  });
  
  Object.defineProperty(this, 'capacity', {
    get: function() { return capacity; },
    set: function(value) {      
      for (var i = 0; i < (this.size - value); i++) {
        var lruItem = findLRU();
        deleteCache(lruItem.key);
      }  
    }
  });
  
  for (key in init) {
    setCache(key, init[key]);
  }  
}

tests.js

var store = new LRUCache(3, {a: 1});
Test.assertEquals(store.size, 1, 'store.size');
Test.assertEquals(store.capacity, 3, 'store.capacity');
Test.assertEquals(store.a, 1, 'store.a');
Test.assertEquals(store.cache('b', 2)['b'], 2, 'store.b');
store.a = 5;
Test.assertEquals(store.a, 5, 'store.a');
store.cache('c', 3).cache('d', 4);
Test.assertEquals(store.b, undefined, 'store.b');
Test.assertEquals(store.c, 3, 'store.c');
Test.assertEquals(store.d, 4, 'store.d');
Test.assertEquals(store.a, 5, 'store.a');
Test.assertEquals(store.size, 3, 'store.size');
Test.assertEquals(store.delete('delete'), false, "store.delete('delete')"); 
Test.assertEquals(store.delete('d'), true, "store.delete('d')");
Test.assertEquals(store.d, undefined, 'store.d');
Test.assertEquals(store.delete('e'), true, "store.delete('e')");
Test.assertEquals(store.size, 2, 'store.size');
store.cache('c', 4);
Test.assertEquals(store.c, 4, 'store.c');
store.capacity = 1;
Test.assertEquals(Object.keys(store).length, 1, "Object.keys(store).length");
Test.assertEquals(Object.keys(store)[0], 'c', "Object.keys(store).length");