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React.js

JSX vs JS: Understanding React Components

By Filip on 04/30/2024

Explore the key differences and use cases of .js and .jsx file extensions in ReactJS development, understanding when to use each for optimal results.

JSX vs JS: Understanding React Components

Table of Contents

Introduction

In the realm of React development, two file extensions, .js and .jsx, play pivotal roles. While both extensions house JavaScript code, they serve distinct purposes and contribute to different aspects of building React applications. This guide delves into the core differences between .js and .jsx files, elucidating their individual functionalities and providing insights into when to employ each effectively.

Step-by-Step Guide

While both file extensions are used within React projects, they serve distinct purposes:

1. .js Files: Pure JavaScript

  • These files contain standard JavaScript code.
  • They are used for logic, functions, data manipulation, and any other tasks that don't involve directly writing UI elements.
  • Example:
// Example.js
function addNumbers(a, b) {
  return a + b;
}

const result = addNumbers(5, 10);
console.log(result); // Output: 15

2. .jsx Files: JavaScript with XML-like Syntax

  • These files are also JavaScript, but they incorporate JSX syntax.
  • JSX allows you to write HTML-like structures directly within your JavaScript code, making it easier to define and manage UI components.
  • JSX gets transpiled into regular JavaScript before it's executed by the browser.
  • Example:
// Example.jsx
const MyComponent = () => {
  return (
    <div>
      <h1>Hello, world!</h1>
      <p>This is a JSX component.</p>
    </div>
  );
};

ReactDOM.render(<MyComponent />, document.getElementById('root'));

Key Differences and When to Use Each:

  • Purpose: Use .js for pure JavaScript logic and functions. Use .jsx for defining React components with JSX syntax.
  • Syntax: .js files use standard JavaScript syntax. .jsx files can include both JavaScript and XML-like syntax for describing UI elements.
  • Readability: JSX can improve the readability and maintainability of your UI code by making it more visually similar to the HTML structure it represents.

Best Practices:

  • Component Structure: It's common to use .jsx for the main component file and .js for separate files containing helper functions or complex logic used by the component.
  • Consistency: Maintain consistency within your project. If you start using JSX, stick with it for your UI components to ensure code clarity.

In essence, understanding the distinction between .js and .jsx files is crucial for effectively structuring and organizing your React projects.

Code Example

The provided code snippets illustrate the distinction between using JavaScript (.js) and JSX (.jsx) in the context of React development. The first example showcases pure JavaScript functions for calculating and displaying the area of a rectangle, demonstrating logic without UI elements. The second example utilizes JSX to define a React component that renders a greeting message, highlighting the use of HTML-like structures within JavaScript for UI development.

Following your provided explanation, let's illustrate the concepts with practical JavaScript examples:

1. Example.js (Pure JavaScript)

// Function to calculate the area of a rectangle
function calculateArea(width, height) {
  return width * height;
}

// Function to display the result in the console
function displayArea(width, height) {
  const area = calculateArea(width, height);
  console.log(`The area of the rectangle is ${area}`);
}

// Calling the functions
displayArea(5, 10); // Output: The area of the rectangle is 50

2. Example.jsx (JavaScript with JSX)

// Importing React library
import React from 'react';

// Defining a functional component with JSX
const Greeting = ({ name }) => {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      <p>Welcome to the world of React and JSX.</p>
    </div>
  );
};

// Rendering the component into the 'root' element of the HTML
ReactDOM.render(<Greeting name="Alice" />, document.getElementById('root'));

Explanation:

  • Example.js: This file demonstrates pure JavaScript functions for calculating and displaying the area of a rectangle. It showcases logic and calculations without any UI elements.
  • Example.jsx: This file utilizes JSX to define a React component called Greeting. The component takes a name prop and renders a greeting message with the provided name. JSX allows us to write HTML-like structures within JavaScript, making the code more intuitive for UI development.

Key Takeaways:

  • Use .js files for pure JavaScript logic, functions, and calculations.
  • Use .jsx files for defining React components with JSX syntax, which simplifies creating and managing UI elements.
  • JSX enhances code readability and maintainability, especially when dealing with complex UI structures.

Remember:

  • JSX requires transpilation (using tools like Babel) before it can be understood by browsers.
  • Maintaining consistency in file extensions within your project is crucial for clarity and organization.

Additional Notes

Deeper Dive into JSX:

  • Expressions in JSX: You can embed JavaScript expressions within JSX using curly braces {}. This allows for dynamic content and logic within your UI elements.
  • Attributes in JSX: Similar to HTML, you can add attributes to JSX elements. However, some attribute names differ (e.g., className instead of class, htmlFor instead of for).
  • Children in JSX: JSX elements can have children, which can be other JSX elements, text, or even JavaScript expressions.

Advanced Concepts:

  • Component Composition: JSX facilitates component composition, allowing you to build complex UIs by nesting and combining smaller components.
  • Styling Components: You can style React components using various methods, including inline styles, CSS classes, and CSS-in-JS libraries.
  • Type Checking with JSX: Tools like TypeScript can be used with JSX to add static type checking, improving code reliability and maintainability.

Beyond the Basics:

  • JSX Alternatives: While JSX is popular, alternative syntaxes like hyperscript exist. However, JSX remains the dominant choice in the React ecosystem.
  • JSX and Performance: JSX itself doesn't impact runtime performance significantly. The transpilation process is efficient, and the resulting JavaScript code is optimized.
  • Community and Resources: The React community offers extensive resources, tutorials, and libraries to support your JSX development journey.

In conclusion, understanding .js and .jsx files is fundamental for effective React development. By leveraging the strengths of each file type and exploring advanced concepts, you can build well-structured, maintainable, and dynamic user interfaces.

Summary

Feature .js Files .jsx Files
Content Pure JavaScript code (logic, functions, etc.) JavaScript with JSX syntax for UI elements
Purpose Non-UI tasks, data manipulation, calculations Defining and managing React components
Syntax Standard JavaScript JavaScript + XML-like syntax for describing UI structure
Readability Code focused on logic Visually similar to HTML, enhancing UI code clarity
Use Cases Helper functions, complex logic, utilities React component definitions

Conclusion

In conclusion, mastering the distinction between .js and .jsx files is fundamental for effective React development. By understanding their unique roles and leveraging their strengths, you can create well-structured, maintainable, and dynamic user interfaces. Remember, .js files excel at handling pure JavaScript logic and functions, while .jsx files, with their JSX syntax, simplify the creation and management of UI elements. By adhering to best practices and exploring advanced concepts, you'll be well-equipped to build exceptional React applications.

References

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