code: function (nextProps, nextState) {
  			return (
  				nextProps.todo !== this.props.todo ||
  				nextProps.editing !== this.props.editing ||
  				nextState.editText !== this.state.editText
  			);
  		}
docs: This is a completely optional performance enhancement that you can
  implement on any React component. If you were to delete this method
  the app would still work correctly (and still be very performant!), we
  just use it as an example of how little code it takes to get an order
  of magnitude performance improvement.