What is Render in React JS? (with Code)

What is Render in React JS- Rendering in React JS is a crucial process in class components that determines how UI elements appear on the screen. The render() method is responsible for returning JSX, which React then converts into actual HTML and displays in the browser.

Understanding the Render Function in React JS

The render() function is a part of class components in React. It is used to return JSX, which React then processes to update the UI efficiently. Unlike functional components that use hooks, class components rely on this method to define their structure and content.

Key Characteristics of the Render Method

• Returns JSX (JavaScript XML) to describe UI components.
• Reads props and state but cannot modify them.
• Must be a pure function without side effects like HTTP requests.
• React calls render() automatically whenever there is a state or prop change.

How ReactDOM.render() Works

ReactDOM.render() is the function responsible for mounting React components into the actual DOM. It takes two arguments:

1. The JSX or component to render (HTML code inside a React component).
2. The target DOM element where the component should be displayed.

Example of ReactDOM.render()

Here, the Welcome component is rendered inside the HTML element with the id="root".

Rendering in Class Components

In class components, the render() method must always return valid JSX or null. Here’s an example of What is Render in React JS:

import React, { Component } from 'react';

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

export default Greeting;

How it Works:

• The render() method reads props and returns JSX.
• When props.name changes, React automatically re-renders the component.

Comparison of Functional and Class Component Rendering

Feature	Functional Component	Class Component
Uses render() method	No	Yes
Uses Hooks	Yes (e.g., useState, useEffect)	No
State Management	Hooks	this.state
Lifecycle Methods	No	Yes

What is State in ReactJS?(3+ easy example)

Common Mistakes to Avoid in Render() Method

Mutating State Directly:

this.state.count = 10; //  Wrong
this.setState({ count: 10 }); // Correct

Using Side Effects in render():

fetch('https://api.example.com/data'); // Avoid in render()

Returning Multiple Elements Without a Wrapper:

return (
  <h1>Hello</h1>
  <p>Welcome to React</p>
); //  Invalid JSX

Instead, use a fragment (<>…):

return (
  <>
    <h1>Hello</h1>
    <p>Welcome to React</p>
  </>
);

Conclusion: What is Render in React JS

The render() function in React JS plays a fundamental role in displaying UI elements in class components. It ensures the application reflects the latest state and prop changes. Understanding how ReactDOM.render() and the render() method work helps in building efficient and error-free React applications.

FAQs