Understanding Rendering In React

April 06, 2023
Understanding Rendering in React



Frameworks and libraries like React, Angular, and Vue help developers build complex, interactive UI components reusable across multiple pages and applications. These tools also help manage state, handle user input, and communicate with backend APIs.

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Rendering Defined

Rendering is a process of generating a view of a user interface based on data. In web development, rendering implies converting HTML, CSS, and JavaScript into visible and interactive pages. In other words, rendering is how the user interface displays on the screen.

How Rendering works in React?

When a user interacts with a React application, the application updates the Virtual DOM. This update triggers reconciliation, where React compares the new Virtual DOM with the previous version and identifies the required changes.

Once React has identified the needed changes, it updates the actual DOM to reflect the new state of the application. This process is known as rendering. React’s rendering engine is highly efficient, and it only updates the parts of the DOM that have changed rather than re-rendering the entire page.

The Virtual DOM Defined

A key concept in React’s rendering process is Virtual DOM. It is a lightweight copy of the actual DOM. When a user interacts with a React application, the application updates the Virtual DOM rather than the actual DOM.

The Virtual DOM is a tree-like structure that represents the user interface. Each node in the tree represents a component, and each component has its state and properties, which dictates its rendering process.

React updates the Virtual DOM to reflect the new state when the component’s state or property changes. This update triggers the process of reconciliation, where React compares the new Virtual DOM with the previous version and identifies the needed changes to the actual DOM.

Reconciliation Defined

Reconciliation implies comparing the new Virtual DOM with the previous version and identifying the changes needed to make to the actual DOM.

React uses a highly efficient diffing algorithm to compare the new Virtual DOM with the previous version. The diffing algorithm compares the nodes in the new Virtual DOM with those in the previous one. If a node in the new Virtual DOM varies from the corresponding node, React updates the actual DOM to reflect the new component state.

Examples of React Render

Basic Component Rendering

Consider a simple example of a React component that renders a button element. The following code defines a Button component that accepts a label prop and renders a button element with the label text:

import React from 'react';

function Button(props) {

  return (

    <button>{props.label}</button>

  );

}

export default Button;

To render this component in a parent component, we can simply import the Button component and include it in the JSX code, passing the label prop as needed. For example:

import React from 'react';

import Button from './Button';

function App() {

  return (

    <div>

      <Button label="Click me!" />

    </div>

  );

}

export default App;

When the App component is rendered, it will display a button element with the label “Click me!”.

Conditional Rendering

React render function allows us to conditionally render components based on certain conditions. Consider the following example of a component that displays a welcome message based on whether a user is logged in or not:

import React from 'react';

function Welcome(props) {

  if (props.isLoggedIn) {

    return <h1>Welcome back, {props.username}!</h1>;

  } else {

    return <h1>Welcome to React Render Function. Please log in.</h1>;

  }

}

export default Welcome;

In the Welcome component, we check the value of the isLoggedIn prop and render a different message depending on whether it is true or false.

To use this component in a parent component, we can pass the isLoggedIn and username props as needed:

import React from 'react';

import Welcome from './Welcome';

function App() {

  const isLoggedIn = true;

  const username = 'John';

  return (

    <div>

      <Welcome isLoggedIn={isLoggedIn} username={username} />

    </div>

  );

}

export default App;

When the App component is rendered, it will display “Welcome back, John!” or “Please log in.” depending on the value of the isLoggedIn prop.

List Rendering

In React render, we can render lists of items using the map method to create an array of components. Consider the following example of a component that renders a list of items:

import React from 'react';

function List(props) {

  const items = props.items.map((item, index) =>

    <li key={index}>{item}</li>

  );

  return (

    <ul>

      {items}

    </ul>

  );

}

export default List;

In the List component, we use the map method to create an array of ‘li’ elements based on the items prop. We include a key prop for each ‘li’ element to help React identify the elements when they are updated.

To use this component in a parent component, we can pass an array of items as the items prop:

import React from 'react';

import List from './List';

function App() {

  const items = ['React render item 1', 'React render item 2', 'React render item 3'];

  return (

    <div>

      <List items={items} />

    </div>

  );

}

export default App;

When the App component is rendered, it will display a list of ‘li’ elements with the values “React render item 1”, “React render item 2”, and “React render item 3”.

The Final Word

In this post, we developed an understanding of React Rendering and how React render function works. Understanding how rendering works in React is essential for building high-quality, performant applications.

Read Also: A Complete Guide To Inline Style In React

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author

jordan

Full Stack Java Developer | Writer | Recruiter, bridging the gap between exceptional talent and opportunities, for some of the biggest Fortune 500 companies.


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