React Hooks are functions that allow you to hook into React lifecycle and state features. They primarily serve as an alternative for classes. They can help in keeping your components clean and perform better. Hooks are a recent  addition in React version 16.8.0.

In this article, we are going to show you how to convert a React class into a functional component using the useState Hook.

Hooks don’t work inside classes because they let you use React without classes. We will use the built-in hooks instead of React lifecycle methods. Eg. useState, useEffect, useRef etc.

We are covering useState, useEffect, useRef React hooks in this article. useState() is used to replace the constructor functions and state declarations. While useEffect() is used to replace componentDidMount() and componentDidUpdate(). You can use useEffect as many times as you need to in single component. And the last one, useRef has another cool usage besides DOM refs, it is also a generic container whose current property is mutable, it also can hold any value similar to an instance property of a class.

Steps to convert a React class component into a functional component using React Hooks –

Step 1. Change ‘class ComponentName extends Component’ With ‘function ComponentName(props)‘

Step 2. Remove “this.” And “this.state” from the entire component.

Step 3. import React, { useState } from ‘react’

Step 4. Remove the constructor. Add its logic as shown above in the image for initializing the state variables with the help of useState hook.

Let’s understand conversion into useState, useEffect and useRef with examples –

• useState() Hook –

The parameter of the useState hook is the initial value of the state. This hook provides the array with two values – the first is the name of the state and the second is the function name which updates the value of that state.

Eg.

const [num, setNum] = useState(0); //declaration

setNum(10) //use

Here num is the state name, setCount is the function that you can use anywhere in the component to update that state.

Here are some examples of setting or initializing state variables for different data types –

//Set an Integer

const [num, setNum] = useState(0);

setNum(10);

//Set a String

const [name, setUsername] = useState(‘John’);

setUsername(‘Smith’);

//Set a Boolean

const [isValid, setIsValid] = useState(false);

setIsValid(true);

//Set and Array

const [items, setItems] = useState([]);

setItems([0,1,2,3,4]);

setItems([{id:0, color:”red”},{id:1, color:”green”},{id:2, color:”blue”}]);

//Set and Object

const [form, setValues] = useState({

id: 0,

firstName: ‘’,

lastName: ‘’,

subscribe: false

})

setValues({

…form,

firstName: ‘Jamie’,

subscribe: true

})

• Replace lifecycle methods (compentDidMount, componentWillUnmount,

 componentWillReceiveProps, componentDidUpdate) with useEffect

e.g.

const [items, setItems] = useState([]);

const [num, setNum] = useState(0);

1. compentDidMount

useEffect(()=>{

setItems(items);

}, [])   // Here empty array indicates don’t look for any updates

b.componentWillUnmount

useEffect(()=>{

return () => {console.log(‘unmounting the component’)}

},[])

c. componentDidUpdate/componentWillReceiveProps

This will get executed when your ‘num’ state variable and ‘id’ props will get updated.

useEffect(()=>{

if (!isEmpty(num))

{

console.log(‘num changed = ’,num);

setItems(items);

}

if(!isEmpty(props.id))

{

console.log(‘props.id changed = ’,props.id);

}

},[num, props.id])

• Use of useRef

const [num, setNum] = useState(0);

const prevNumRef = useRef();

useEffect(()=>{

prevNumRef.current = num;

})

const prevNum = prevNumRef.current;

return <h1>Current value : {num}, previous value = {prevNum}</h1>

Advantages

1.With React hooks, the component will be cleaner and easier to read (fewer lines of code). Hooks are easier to work with and to test.

2.It is easy to make code reusable. They don’t create another element in DOM like HOCs in React do.

3. useState – it allows to update different states with specific functions. The ability to move the state update logic as a separate hook.

Disadvantages

1.useEffect hook allows to merge three lifecycle methods such as componentDidMount, componentWillUnmount and componentDidUpdate into one and the issue with useEffect is the second parameters ,i.e. the array that we need to pass to define this behaviour. It is not explicit enough.

2.React Hooks are new additions to React. So to convert and test a complex class can be a time-consuming task initially .

3.Since it is relatively a new addition it may not be compatible with all third party libraries. But this is rapidly changing .

This is all about React Hooks in a nutshell. If you are looking to build any a mobile or web application using React technology, then please contact us.

Happy coding!

Now, let’s understand – what is TypeScript?

TypeScript is an open-source programming language maintained and developed by Microsoft since 2012. It is a set of tools which uses a strongly typed, object-oriented and compiled language. It is an extended JavaScript programming language with additional features. When a new developer joins the team and uses any existing component of the project, he can easily understand its props with their specific types.

According to GitHub, TypeScript is one of the fastest-growing technologies. It is downloaded 31 Million times per month. Developer survey results of 2019 on stack overflow, place TypeScript at 10th position for “Most popular technology” and 3rd position for “Most Loved technology”. So as a new developer, it is not something which you can ignore.

When to use TypeScript?

Development teams working together on coding projects can struggle with code complexity, particularly as projects increase in size. TypeScript is recommended for large projects as it is the best option for maintaining code quality. It enables self-explanatory code right from the initial stages of the project.

Some of the significant features of TypeScript are listed below:

1. Static typing –
The static typing feature is one of the common reasons for developers to migrate their existing project from JavaScript to TypeScript. You can add data-types for variables, functions, properties, interfaces, etc, and it indicates warnings and errors regarding data type issues even before the compilation. I think that’s a wonderful feature because as a young developer, I faced a lot of problems while doing scripting.

Note: Static typing is optional.

2. Object-oriented –
TypeScript supports object-oriented programming, i.e. you can use class, Inheritance, Encapsulation, and Polymorphism.

3. Code suggestion –
It is best to use TypeScript with the IDEs since IDEs provide features such as IntelliSense and error highlighting.
If a developer wants to access the component props {this.props.}, then Typescript suggests all the available props, and highlights any typos.

4. Display errors/warnings ASAP –
TypeScript highlights the errors immediately.

5. TypeScript is portable –
All companies have a different kind of IT infrastructure set-up, with different operating systems and browsers. The advantage of TypeScript is that it is a superset of Javascript, meaning it can run on any environment that Javascript runs on. It is portable across operating systems and browsers.

How to create a new React JS project enabled by Typescript? –
To create a new project which is enabled by Typescript, you can use the following command.
e.g. npx create-react-app <> –TypeScript

It creates tsconfig.json which has typescript configurations.
tsconfig.json
{
“compilerOptions”: {
“target”: “es5”,
“lib”: [
“dom”,
“dom.iterable”,
“esnext”
],
“allowJs”: true,
“skipLibCheck”: true,
“esModuleInterop”: true,
“allowSyntheticDefaultImports”: true,
“strict”: true,
“forceConsistentCasingInFileNames”: true,
“module”: “esnext”,
“moduleResolution”: “node”,
“resolveJsonModule”: true,
“isolatedModules”: true,
“noEmit”: true,
“jsx”: “react”
},
“include”: [
“src”
]
}

Here, you can find the set of rules defined for the project. You can also modify or add more constraints if you want.

How to add TypeScript to the existing React JS project?
To add TypeScript in the existing project, you will have to install TypeScript and other required types externally
e.g. npm install –save TypeScript @types/node @types/react @types/jest @types/react-dom

After this, two changes are needed in the projects:
– First, rename all the “.js” file to “.ts” or “.tsx”
– Secondly, create a tsconfig.json in the root directory with the set of rules mentioned in the first step.

Happy Coding!!