Question: With the introduction of [hooks](https://reactjs.org/docs/hooks-intro.html) in React, the main confusion now is when to use function components with hooks and class components because with the help of hooks one can get `state` and partial `lifecycle hooks` even in function components. So, I have the following questions

* What is the real advantages of hooks?
* When to use function components with hooks vs Class components?

For example, function components with hooks can't help in perf as class components does. They can't skip re-renders as they don't have `shouldComponentUpdate` implemented. Is there anymore reasons?

Thanks in advance.

Answer: 
The idea behind introducing `Hooks` and other features like `React.memo` and `React.lazy` is to help reduce the code that one has to write and also aggregate similar actions together.

The docs mention few really good reason to make use of Hooks instead of classes

**It’s hard to reuse stateful logic between components** Generally when you use HOC or renderProps you have to restructure your App with multiple hierarchies when you try to see it in DevTools, Hooks avoid such scenarios and help in clearer code

**Complex components become hard to understand** Often with classes Mutually unrelated code often ends up together or related code tends to be split apart, it becomes more and more difficult to maintain. An example of such a case is event listeners, where you add listeners in `componentDidMount` and remove them in `componentWillUnmount` . Hooks let you combine these two

**Classes confuse both people and machines** With classes you need to understand binding and the context in which functions are called, which often becomes confusion.

> 
> function components with hooks can't help in perf as class
> components does. They can't skip re-renders as they don't have
> shouldComponentUpdate implemented.
> 
> 
> 

Function component can be memoized in a similar way as `React.PureComponent` with Classes by making use of `React.memo` and you can pass in a comparator function as the second argument to `React.memo` that lets you implement a custom comparator

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The idea is to be able write the code that you can write using React class component using function component with the help of `Hooks` and other utilities. Hooks can cover all use cases for classes while providing more flexibility in extracting, testing, and reusing code.

Since hooks is not yet fully shipped, its advised to not use hooks for critical components and start with relatively small component, and yes you can completely replace classes with function components

---

However one reason that you should still go for Class components over the function components with hooks until Suspense is out for data fetching. Data fetching with useEffect hooks isn't as intuitive as it is with lifecycle methods.

Also @DanAbramov in one of his tweets mentioned that hooks are designed to work with Suspense and until suspense is out it's better to use Class
Hooks greatly reduce the amount of code you need to write and increase its readability.

It is worth noting though that there are hidden processes going on behind (Just like component did mount etc.) that mean if you don't understand what is going on it can be difficult to troubleshoot. It is best to experiment with them and read through the docs fully before implementing on a live project.

Also there is still limited support/documentation for testing hooks compared to classes.
<https://dev.to/theactualgivens/testing-react-hook-state-changes-2oga>

**Update 28/08/2020**
Use the react hooks testing library with custom hooks for testing
<https://github.com/testing-library/react-hooks-testing-library>