Discussion on: How to use useReducer hook to mimic setState method?

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Your approach to state handling is incorrect. The power of useState comes from the possibility to split state into smaller chunks. So you don't have to store objects at all, like the way you did it. In fact, you can create something like this:

const [name, setName] = useState('John');
const [age, setAge] = useState(25);
const [isLoading, setIsLoading] = useState(true);

With this approach you get more flexibility. So your use case of useReducer is incorrect in assumptions. Furthermore, with my suggested approach you get more power when controlling data changes and responding to them with useEffect hook.

Andrey • May 29 '20

Your state might arrive from an external source as a complete object. You may also have a 'table' component which renders and manages the state of the entire table. So complex objects is a state are actually very usual.

Deric Cain • Oct 17 '19

To say his approach is "incorrect" is incorrect. It is just that, an approach. It is the method by which he chose to solve a problem. There is nothing in the React docs that says this is "incorrect" and there are no facts that back up that this approach is "incorrect". It's okay to disagree with an approach and prefer another approach, but I would be careful of making factual statements when really you are stating an opinion.

Łukasz Wolnik • Jun 27 '19

Both approaches have their use cases.

In a large-scale app it would be simply to cumbersome to explicitly set useStatefor each of the state variables. So I would use useReducer in that case.

Piotr Nalepa • Jun 27 '19

When there is too many state variables in a component, then it might be a sign that a component can be splitted into smaller ones. But it depends on a use case.

Łukasz Wolnik • Jun 27 '19

I agree with you. It might be the case, so it's good to have options and make informed trade-offs.

Przemek Wolnik • Jun 27 '19 • Edited

Hi @sunpietro , thank you for your comment!

Firts of all the goal of this post was to show how to mimic setState method with useReducer hook (mostly for fun as I mentioned in the post).

I also wanted to show that one doesn't have to use actions, switch statement, payloads etc. while using useReducer hook (like we do with Redux).

I totally agree that one of the advantages of hooks is the posibility to split and compose chunks of code the way it is convinent for the programmer. You rarely have to do something. More often you can if you like.

Having said that using useReducer makes sense when you want to keep in state variables that are related to each other. E.g. imagine that you have form with dozens of fields and you want to implement reset functionality. Using useState means you have to remember to manually reset every single field one by one:

setName('');
setSurname('');
setEmail('');
setPassowrd('');
setStreet('');
setAge(18);

With useReducer you can do the same thing like this:

setState({
  name: '',
  surname: '',
  email: '',
  password: '',
  street: '',
  age: 18,
});

The more you have to remember and do manually the bigger possibiity of bug (to say nothing about how tedious it might be).

If you happen to use TypeScript the advantage of the second approach is even bigger (e.g. you'll get an error if you forget to reset some field).

Again the goal of this post was not to show how to use useState vs useReducer

So hopefully my approach wasn't that bad after all? :)

Alfredo Salzillo • Jun 27 '19

The more you have to remember and do manually the bigger possibiity of bug (to say nothing about how tedious it might be). >

In your example, if you add another property, for example, the 'Middle Name', you have to add a row in either the cases (using multiple set or a setState).
The number of things to remember is the same, so the 'possibility' of a mistake is the same.

Przemek Wolnik • Jun 27 '19

@alfredosalzillo yes but having them groupped in one object means: they are connected to each other.

const [formData, setFormData] = useReducer(reducer, {
  name: 'Bob',
  surname: 'Smith',
  password: 'pass',
  age: 18,
});
const [someOtherVar, setSomeOtherVar] = useState(125);

This way I don't have to remember which state variables should be changed. I can take a look at initial formData object and see all properties that need to be reset.

Deric Cain • Oct 17 '19

I totally agree with you. For instance, say you have a form with a few inputs. When you go to submit that form, if you are using useState, then you have to create an object with all of the fields in order to submit the data. Sure... no big deal, but when using useReducer, you simply submit your state because it is already an object.

Anyone saying that you are "doing it wrong" is, well.... wrong. There is no rule that says you can't use useReducer just like you are using it in this example. I actually prefer it and if it works easier for you, then "you are doing it right" (especially since there are no perf hits and nothing wrong syntactically).