simple-lru.js
function () {
      var count = 0
        , tail = this._tail
        , head = this._head
        , keys = new Array(this._len);

      for (var i = tail; i < head; i++) {
        var entry = this._byOrder[i];
        if (entry) keys[count++] = entry.key;
      }

      return keys;
    }
function () {
      var count = 0
        , tail = this._tail
        , head = this._head
        , keys = new Array(this._len);

      for (var i = tail; i < head; i++) {
        var entry = this._byOrder[i];
        if (entry) keys[count++] = entry.key;
      }

      return keys;
    }
function ( ) { var count = 0 , tail = this . _tail , head = this . _head , keys = new Array ( this . _len ) ; for ( var i = tail ; i < head ; i ++ ) { var entry = this . _byOrder [ i ] ; if ( entry ) keys [ count ++ ] = entry . key ; } return keys ; }
return array of keys in least recently used order
@return {Array}
return array of keys in least recently used order