code: function getGesture( element_ ) {
      const element = ensureDom( element_ );
      if ( !element[ SYMBOL ] ) element[ SYMBOL ] = new Gesture( element );
      return element[ SYMBOL ];
  }
docs: Return the associated gesture object. If it does not exist, create it.
  
  @param   {[type]} element_ [description]
  @returns {[type]}         [description]