code: function (property, callback) {
          // if only one arg we count the collection
          if ([].slice.call(arguments).length === 1) {
              callback = property 
              property = 'key'
          } 
          var c = 0 
          this.each(function(e){
              if (e[property]) c++
          })
          this.fn('count', callback).call(this, c)
      }
docs: count of rows in the lawnchair collection with property