Get Started with ReactJS: A Beginner's Guide
Tags: programming, react, beginners, tutorial
Published: 2022-10-28 00:45:34


![Introduction to ReactJs](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ufu6ew0p6h1ieff1lcs0.png)

## What is React?

React is a JavaScript library for building user interfaces. It is maintained by Facebook and a community of individual developers and companies. React can be used as a base in the development of single-page or mobile applications.

React allows developers to create large web applications that can change data, without reloading the page. The goal of React is to provide a way to create fast web applications that are scalable.

React is a JavaScript library for building user interfaces.

## The Benefits of React

React is known for its speed, scalability, and simplicity. The main benefit of React is its performance.

React is able to handle large amounts of data quickly and efficiently.This makes React a good choice for developing large scale applications.

It's declarative syntax makes code easy to read and maintain, while its virtual DOM ensures fast performance. React is also well-suited for large applications with complex data structures. 

Here are some other advantages of React that make it a great choice for web development: 

- JSX makes templating easier and more concise

- It lets you create reusable components so that your code is easy to read and maintain. 

- React js is advantageous because of its simplicity, flexibility, and scalability. 

- Additionally, working with the Reactjs framework helps to improve team collaboration and communication.
 
- React can be used for creating single-page applications.

- It's declarative: React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes.

## React JSX

React is unique because it uses a declarative paradigm and JavaScript syntax extension called JSX. This makes code more readable and helps make development easier.

JSX is a syntax extension for React that allows you to write markup directly in your JavaScript code.

```
const myElement = <h1>I Love JSX!</h1>;

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(myElement);
```
Without JSX:

```
const myElement = React.createElement('h1', {}, 'I do not use JSX!');

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(myElement);
```

JSX is an XML-like syntax extension to ECMAScript without any defined semantics. It's NOT intended to be implemented by engines or browsers.

It's NOT a specification. It's intended to be used by various preprocessors (transpilers) to transform these tokens into standard ECMAScript.

JSX is a syntax extension of JavaScript that lets you write HTML-like syntax within your JavaScript code. With React, you can use either regular JavaScript or JSX.

## React Components

### React Class Component

React class components are one of the ways that you can create React components. They are created by extending the React.Component class. 

In a React class component, you will need to create a render() method. The render() method will return a React element.

When creating a class component, you need to extend the React.Component class.This gives your component the ability to have state and lifecycle methods. 


Class components are also easy to test, because they are just JavaScript classes.They allow you to use JavaScript classes to create React components. 

Class components are more powerful than functional components and they can have state. They make it easy to create reusable code, and they are great for working with larger applications.

React introduced official support for class components in version 15.5. Class components are a more traditional way of writing React components using a class. They can be used with React’s new context API and static getDerivedStateFromProps lifecycle methods. 

Class components should be used when you need to use one of these features or the other capabilities unique to classes, such as local state or access to lifecycle methods.

```
class Welcome extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}
```

### React Function Component

Function components are a simpler way to write React components. They are equivalent to stateless functional components in React.
 
Simply put, function components are functions that return React elements. When you need a component that doesn’t have state, you can use a function component.

A function component is a simple functional unit used to create React components. It accepts props and returns a React element.
 
When you create a React component, you have the option of either creating a function component or a class component. 

A function component is a React component that is written as a JavaScript function. 

Function components are simpler than class components, and they are often used for presentational components.

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

## React Props

React Props provide a way for a parent component to pass data to a child component. The child component can then access that data via the this.props object. 

React Props are also used to specify the behavior of a component, such as whether it should be rendered or not. 

React props are pieces of data that are passed into React components. They're used to customize the behavior of a component, and they can be used in conjunction with state to manage the data within a component. 

React props are immutable, meaning they can't be changed once they're set.

This makes them perfect for passing data down the component tree, and it helps to keep your components modular and easy to reason about.

```
function Person(props) {
  return <h2>I'm { props.name }!</h2>;
}

function Greeting() {
  const name = "Jesse"
  return (
    <>
      <h1>Hello!</h1>
      <Person name=
{
 name 
}
 />
    </>
  );
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Greeting />);
```

## React State

React state is one of the most important concepts in React. 
It refers to the data that a React component needs in order to render itself. 

## Creating the state Object

The state object is initialized in the constructor:

```
class Car extends React.Component {
  constructor(props) {
    super(props);
    this.state = {brand: "Ford"};
  }
  render() {
    return (
      <div>
        <h1>My Car</h1>
      </div>
    );
  }
}
```
React state can be used to store data that a component needs in order to render itself. 

When a component's state changes, the component will re-render itself. There are two ways to change a component's state: setState and forceUpdate.

```
class Car extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      brand: "Ford",
      model: "Mustang",
      color: "red",
      year: 1964
    };
  }
  changeColor = () => {
    this.setState({color: "blue"});
  }
  render() {
    return (
      <div>
        <h1>My {this.state.brand}</h1>
        <p>
          It is a {this.state.color}
          {this.state.model}
          from {this.state.year}.
        </p>
        <button
          type="button"
          onClick={this.changeColor}
        >Change color</button>
      </div>
    );
  }
}
```

React setState is a function used to update the state of a React component. The function takes two arguments, the first being an object containing the new state values and the second being a callback function. 
The callback function is executed after the new state values have been applied. The new state values are merged with the previous state values.

React forceUpdate is a function that causes a component to re-render. 
This can be useful if you need to make a change to a prop or state that will cause the component to look different. 
forceUpdate will not call shouldComponentUpdate, so it is not suitable for all situations. Use it sparingly!

```
class App extends React.Component {  
constructor() {  
super();        
this.state = {  
message: "Hello World"  
};      
this.updateSetState = this.updateSetState.bind(this);  
}  
updateSetState() {  
this.setState({  
message:"It is a beautiful day."  
});  
}  
render() {  
return (  
<div>  
<h1>{this.state.message}</h1>  
<button onClick = {this.updateSetState}>SET</button>  
</div>  
);  
}  
}  
```
In the example above, the data displayed is updated from "Hello World" to "It is a beautiful day." on button click
 

When a developer wants to update the view in React, they call the forceUpdate function. This function tells React that the component needs to be re-rendered.

When the forceUpdate function is called, React will re-render the component, even if the component's props or state haven't changed. 
The forceUpdate function is used when a change happens outside of the component, such as an event listener firing or a request from an API returning data.

React state is a powerful concept that allows developers to easily manage data within their React applications.

By using state, developers can create complex applications that are responsive to user input and can change over time.

React state is easy to use and can be a great way to improve the performance of your application.

## Rendering a React Component

In order to display a React component, you must first "render" the component. This simply means that you need to output the correct HTML code from your React component so that it can be displayed in the browser. 

The process of rendering a React component is actually quite simple. First, you create a new React element. This element can be either a DOM element or a custom React component. 

```
<div id="root"></div>
```

Once you have created your element, you use the ReactDOM. This library will allow you to render your React component into an HTML element on the page. 

```
const root = ReactDOM.createRoot(
  document.getElementById('root')
);
const element = <h1>Hello, world</h1>;
root.render(element);
```

Once you have rendered your component, you can then interact with it using the ReactDOM API.

## Updating a Rendered React Component

In the past, when a React component was rendered, it was static. Once rendered, the component couldn't be changed. 

This made it difficult to update components that needed to change based on user interaction or new data. 

However, now there is a way to update a rendered React component. By using the setState method, a developer can change the component after it has been rendered. 

This makes it possible to create dynamic and interactive user interfaces with React.

When building applications with React, it is important to be able to update a rendered component. 

There are two ways to do this: with the component’s state or props. Updating the state of a component will cause the component to re-render, and updating the props of a component will cause the component to update. 

```
	
class App extends Component {
constructor(props){
	super(props)
		
	// Set initial state
	this.state = {greeting :
		'Click the button to receive greetings'}
		
	// Binding this keyword
	this.updateState = this.updateState.bind(this)
}
	
updateState(){
	// Changing state
	this.setState({greeting :
				'GeeksForGeeks welcomes you !!'})
}
	
render(){
	return (
	<div>
	<h2>Greetings Portal</h2>
	<p>{this.state.greeting}</p>
	
		{/* Set click handler */}
		<button onClick={this.updateState}>
		Click me!
		</button>
	</div>
	)
}
}

```

In order to update a rendered React component, you will need to use the setState method. This method will take in an object that contains the new data that you want to update the component with.
 
Once you have updated the component's state, the component will re-render with the new data. If you need to make a API call in order to fetch new data, you can do so inside of the setState method.

## Conclusion

In conclusion, ReactJS is a great tool for building user interfaces. It is fast, efficient, and easy to learn. If you are looking for a way to get started with ReactJS, this guide is a great place to start.