code: function ( callback ) {
  					self.api.call( _.extend( params, continueParams ), function ( err, data, next ) {
  						if ( err ) {
  							callback( err );
  						} else {
  							// append batch data
  							const batchData = ( typeof key === 'function' ) ? key( data ) : data[ key ];
  
  							res = res.concat( batchData );
  
  							// more pages?
  							continueParams = next;
  							callback( next ? null : true );
  						}
  					} );
  				}
docs: run as long as there's more data