Tag: React Hooks Rules

ReactJS – How to Effectively Think In React Hooks ?

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In this article, we will understand about the rules of React Hooks and how to effectively start using them in our projects. We will discuss the two most important rules of React Hooks and how to effectively think in Hooks.

” React Hooks are a new addition in React 16.8 that let you use state and other React features without writing a class component. In other words, Hooks are functions that let you “hook into” React state and lifecycle features from function components. (They do not work inside class components.)”

A famous quote about learning is :

” The more I live, the more I learn. The more I learn, the more I realize, the less I know. “

So Let’s begin.


What is React Hook?

Hooks are a new addition in React 16.8. They let you use state and other React features without writing a class. It mainly uses to handle the state and side effects in react functional component. React Hooks are a way to use stateful functions inside a functional component. Hooks don’t work inside classes — they let you use React without classesReact provides a few built-in Hooks like useState and useEffect. The React hooks do :

  • Best practices
  • Easy to under understand
  • Easy to test
  • Increases the performance and so on.


Why React Hook?

There are two reasons to use React hooks :

  • The first main reason is the Introduce state in a functional component. We know that the states cannot be used in functions. But with hooks, we can use states.
  • Another reason is the handle side effect in react component. It means, now we can use newly introduced state such as useEffect.

But do we should know for some scenarios, there are 3 places where react fails. While Reuse logic between components :

  • Has Huge components
  • Confusing


Rules Of React Hooks

Hooks are JavaScript functions, but we need to follow two rules when using them :

  1. Call Hooks at the top level;
  2. Only call Hooks from React components.

Let’s look at these rules in more detail :


1. Call Hooks At The Top Level

Don’t call Hooks inside loops, conditions, or nested functions. Always use Hooks at the top level of your React function. By following this rule, we ensure that Hooks are called in the same order each time a component renders. That’s what allows React to correctly preserve the state of Hooks between multiple useState and useEffect calls.

Let’s make a Form component which will have two states:

  • accountName
  • accountDetail

These states will have default values, we’ll make use of the useEffect hook to persist the state to either the local storage of our browser or to the title of our document.

Now, this component will be maybe to successfully manage its state if it remains the same between multiple calls of useState and useEffect.

function Form() {
  // 1. Use the accountName state variable
  const [accountName, setAccountName] = useState('Arun');

  // 2. Use an effect for persisting the form
  useEffect(function persistForm() {
    localStorage.setItem('formData', accountName);
  });

  // 3. Use the accountDetail state variable
  const [accountDetail, setAccountDetail] = useState('Active');

  // 4. Use an effect for updating the title
  useEffect(function updateStatus() {
    document.title = accountName + ' ' + accountDetail;
  });

  // ...
}

If the order of our Hooks changes (which can be possible when they are called in loops or conditionals), React will have a hard time figuring out how to preserve the state of our component.

// ------------
useState('Arun')           // 1. Initialize the accountName state variable with 'Arun'
useEffect(persistForm)     // 2. Add an effect for persisting the form
useState('Active')        // 3. Initialize the accountdetail state variable with 'Active'
useEffect(updateStatus)     // 4. Add an effect for updating the status

// -------------
// Second render
// -------------
useState('Arun')           // 1. Read the accountName state variable (argument is ignored)
useEffect(persistForm)     // 2. Replace the effect for persisting the form
useState('Active')        // 3. Read the accountDetail state variable (argument is ignored)
useEffect(updateStatus)     // 4. Replace the effect for updating the status

// ...

That’s the order React follows to call our hooks. Since the order remains the same, it will be able to preserve the state of our component. But what happens if we put a Hook call inside a condition?

// We're breaking the first rule by using a Hook in a condition
  if (accountName !== '') {
    useEffect(function persistForm() {
      localStorage.setItem('formData', accountName);
    });
  }

The accountName !== '' condition is true on the first render, so we run this Hook. However, on the next render the user might clear the form, making the condition false. Now that we skip this Hook during rendering, the order of the Hook calls becomes different:

useState('Arun')           // 1. Read the accountName state variable (argument is ignored)
// useEffect(persistForm)  // This Hook was skipped!
useState('Active')        // 2 (but was 3). Fail to read the accountDetails state variable
useEffect(updateStatus)     // 3 (but was 4). Fail to replace the effect

React wouldn’t know what to return for the second useState Hook call. React expected that the second Hook call in this component corresponds to the persistForm effect, just like during the previous render — but it doesn’t anymore. From that point on, every next Hook call after the one we skipped would also shift by one — leading to bugs.

This is why Hooks must be called on the top level of our components. If we want to run an effect conditionally, we can put that condition inside our Hook.


2. Only Call Hooks From React Components

Don’t call Hooks from regular JavaScript functions. Instead, you can call Hooks from React function components. Let’s take look at the difference between JavaScript function and React component below:

JavaScript Function

import { useState } = "react";

function toCelsius(fahrenheit) {
  const [name, setName] = useState("Arun");
  return (5/9) * (fahrenheit-32);
}
document.getElementById("demo").innerHTML = toCelsius;

Here we import the useState hook from the React package, and then declared our function. But this is invalid as it is not a React component.

React Function


import React, { useState} from "react";
import ReactDOM from "react-dom";

function Account(props) {
  const [name, setName] = useState("Arun");
  return <p>Hello, {name}! The price is <b>{props.total}</b> and the total amount is <b>{props.amount}</b></p>
}
ReactDom.render(
  <Account total={20} amount={5000} />,
  document.getElementById('root')
);

Even though the body of both looks similar, the latter becomes a component when we import React into the file. This is what makes it possible for us to use things like JSX and React hooks inside.

If we happened to import our preferred hook without importing React (which makes it a regular function), we will not be able to make use of the Hook we’ve imported as the Hook is accessible only in React component.


Call Hooks From Custom Hooks

A custom Hook is a JavaScript function whose name starts with use and that may call other Hooks. For example, useUserName is used below a custom Hook that calls the useState and useEffect hooks. It fetches data from an API, loops through the data, and calls setIsPresent() if the specific username it received is present in the API data.

export default function useUserName(userName) {
  const [isPresent, setIsPresent] = useState(false);
  
  useEffect(() => {
    const data = MockedApi.fetchData();
    data.then((res) => {
      res.forEach((e) => {
        if (e.name === userName) {
          setIsPresent(true);
        }
     });
    });
  });
    
  return isPresent;
}

We can then go on to reuse the functionality of this hook in other places where we need such in our application. In such places, except when needed, we don’t have to call useState or useEffect anymore.

By following this rule, we ensure that all stateful logic in a component is clearly visible from its source code.


Function Component Vs Class Component In Hooks

Let’s take a brief look at class components and functional components (with Hooks), before diving into the few Hooks best practices.

The simplest way to define a component in React is to write a JavaScript function that returns a React element:

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

The Welcome component accepts props which is an object that contains data and returns a React element. We can then import and render this component in another component.

The class component uses a programming methodology called Encapsulation which basically means that everything relevant to the class component will live within it. Life-cycle methods (constructors, componentDidMount(), render, and so on) give components a predictable structure.

Encapsulation is one of the fundamentals of OOP (Object-Oriented Programming). It refers to the bundling of data within the methods that operate on that data, and is used to hide the values or state of a structured data object inside a class — preventing unauthorized parties’ direct access to them.

With Hooks, the composition of a component changes from being a combination of life-cycle Hooks — to functionalities with some render at the end.


Function Component

The example below shows how custom Hooks can be used in a functional component (without showcasing what the body is). However, what it does or can do is not limited. It could be instantiating state variables, consuming contexts, subscribing the component to various side effects — or all of the above if you’re using a custom hook!

function {
  useHook{...};
  useHook{...};
  useHook{...};
  return (
    ...
  );
}


Class Component

A class component requires you to extend from React.Component and create a render function which returns a React element. This requires more code but will also give you some benefits.

class {
  constructor(props) {...}
  componentDidMount() {...}
  componentWillUnmount() {...}
  render() {...}
}

There are some benefits you get by using functional components in React:

  1. It will get easier to separate container and presentational components because you need to think more about your component’s state if you don’t have access to setState() in your component.
  2. Functional components are much easier to read and test because they are plain JavaScript functions without state or lifecycle-hooks.
  3. You end up with less code.
  4. The React team mentioned that there may be a performance boost for functional components in future React versions.

This leads to the first best practice when using React Hooks.


Hooks Best Practices

There are some best practices in writing Hooks the right and effective way as below:

  1. Simplify Your Hooks
  2. Organize And Structure Your Hooks
  3. Use React Hooks Snippets
  4. Put Hooks Rules into Consideration


1. Simplify Your Hooks

Keeping React Hooks simple will give us the power to effectively control and manipulate what goes on in a component throughout its lifetime. Avoid writing custom Hooks as much as possible; we can inline a useState() or useEffect() instead of creating our own hook.

If we find ourself making use of a bunch of custom Hooks that are related in functionality, we can create a custom hook that acts as a wrapper for these. Let’s take a look at two different functional components with hooks below.

Functional Component v1

function {
  useHook(...);
  useHook(...);
  useHook(...);
  return(
    <div>...</div>
  );
}

Functional Component v2

function {
  useCustomHook(...);
    useHook(...);
    useHook(...);
  return(
    <div>...</div>
  );
}

v2 is a better version because it keeps the hook simple and all other useHooks are inline accordingly. This allows us to create functionality that can be reused across different components and also gives us more power to control and manipulate our components effectively. Instead of adopting v1 in which our components are littered with Hooks, we should make use of v2 which will make debugging easy and our code cleaner.


2. Organize And Structure Your Hooks

One of the advantages of React Hooks is the ability to write less code that is easy to read. In some cases, the amount of useEffect() and useState() can still be confusing. When we keep our component organized it will help in readability and keep the flow of our components consistent and predictable. If our custom Hooks are too complicated, we can always break them down to sub-custom Hooks. Extract the logic of our component to custom Hooks to make our code readable.


3. Use React Hooks Snippets

React Hooks Snippets is a Visual Studio Code extension to make React Hooks easier and faster. Currently, five hooks are supported:

  • useState()
  • useEffect()
  • useContext()
  • useCallback()
  • useMemo()

There are two ways (Command and Extension Marketplace) we can add React Hooks snippets to our project:


4. Put Hooks Rules into Consideration

Endeavor to always put the two rules of Hooks we learned earlier into consideration while working with React Hooks.

  • Only call your Hooks at the top level. Don’t call Hooks inside loops, conditions or nested functions.
  • Always call Hooks from React function components or from custom Hooks, don’t call Hooks from regular JavaScript functions.

The ESlint plugin called eslint-plugin-react-hooks enforces these two rules, we can add this plugin to your project if we’d like it as we explain above in rules of hooks section.

Best practices have not been fully resolved because Hooks are still relatively new. So adoption should be taken with precaution one would take in adopting in any early technology. With that in mind, Hooks are the way for the future of React.

That’s all about in this article.


Conclusion

In this article, We understood about the two most important rules of React Hooks and how to effectively think in Hooks. We looked at functional components and some best practices in writing Hooks the right and effective way. As brief as the rules are, it’s important to make them our guiding compass when writing rules. If we are prone to forget it, we can make use of the ESLint plugin to enforce it.

Thanks for reading ! I hope you enjoyed and learned about the Hook Concepts in ReactJS. Reading is one thing, but the only way to master it is to do it yourself.

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