index.js
function(data, done) {
      this._data.push(this._clone(data));
      var ret = this._data.length;
      done(null, ret);
    }
function(data, done) {
      this._data.push(this._clone(data));
      var ret = this._data.length;
      done(null, ret);
    }
function ( data , done ) { this . _data . push ( this . _clone ( data ) ) ; var ret = this . _data . length ; done ( null , ret ) ; }
add an item to the store
@param  {Object}   data    The item to store
@param  {Function} done The callback when done
add an item to the store