code: function (i) {
        return function (e) {
          if (this.props.disabled) return;
          var position = this._getMousePosition(e);
          this._start(i, position[0]);
          this._addHandlers(this._getMouseEventMap());
          pauseEvent(e);
        }.bind(this);
      }
docs: create the `mousedown` handler for the i-th handle