Building Secure and Maintainable UIs in React: Alternatives to Raw HTML

• React typically uses JSX (JavaScript Syntax Extension) to describe the UI structure. JSX is a blend of HTML-like syntax and JavaScript expressions, allowing you to create components.
• However, there are scenarios where you might need to render raw HTML content fetched from an API, a database, or user input.

Approaches to Render Raw HTML:

1. Using Unicode and UTF-8 Encoding (Safest):

   • If your HTML content contains special characters, ensure it's saved as a UTF-8 encoded file. UTF-8 is a universal character encoding that supports a wide range of characters.
   • In your React component, you can directly include the HTML content within curly braces ({}) in your JSX, as React will treat it as a string:

   import React from 'react';
   
   function MyComponent() {
     const htmlContent = '<b>This is bold text</b> using UTF-8 encoding.';
     return (
       <div dangerouslySetInnerHTML={{ __html: htmlContent }} />
     );
   }
   

2. dangerouslySetInnerHTML (Use with Caution):

   • This approach directly inserts the HTML string into the DOM using the dangerouslySetInnerHTML property. It's the most convenient method, but it comes with security risks:
     • XSS (Cross-Site Scripting) Vulnerability: If the HTML content isn't sanitized, it could contain malicious scripts that execute in the user's browser when rendered.
   • Use this method only if you absolutely trust the source of your HTML content and have thorough sanitization mechanisms in place.

   import React from 'react';
   import { DOMPurify } [Library for sanitization]
   
   function MyComponent() {
     const htmlContent = '<b>This is bold text</b> with <script>alert("XSS attack!");</script>.'; // Untrusted source
     const sanitizedContent = DOMPurify.sanitize(htmlContent); // Sanitize (replace the library with your chosen one)
     return (
       <div dangerouslySetInnerHTML={{ __html: sanitizedContent }} />
     );
   }
   

3. Alternative Approaches (Consider These First):

Choosing the Right Method:

• For simple, trusted HTML content: Unicode and UTF-8 encoding is the safest option.
• For untrusted HTML content (use with caution): Employ dangerouslySetInnerHTML only after thorough sanitization using a library like DOMPurify.
• Generally: If there are viable alternatives using React components or controlled components, consider those first to avoid security risks and maintain better control over your UI.

Important Considerations:

• Security: Sanitize untrusted HTML content rigorously before using dangerouslySetInnerHTML.
• Performance: Large HTML strings might affect performance. Consider alternative approaches if performance is critical.
• Maintainability: Complex HTML content might be harder to maintain within components. Evaluate if component-based approaches offer better maintainability.

Example Codes for Rendering Raw HTML with React:

import React from 'react';

function MyComponent() {
  const htmlContent = '<b>This is bold text</b> using UTF-8 encoding.';
  return (
    <div>{htmlContent}</div> // Directly include within curly braces
  );
}

Explanation:

• This approach assumes the htmlContent is already encoded in UTF-8.
• React renders the HTML content as a string without any special interpretation.

import React from 'react';
import DOMPurify from 'dompurify'; // Example sanitization library

function MyComponent() {
  const htmlContent = '<b>This is bold text</b> with <script>alert("XSS attack!");</script>.'; // Untrusted source
  const sanitizedContent = DOMPurify.sanitize(htmlContent); // Sanitize (replace with your chosen library)
  return (
    <div dangerouslySetInnerHTML={{ __html: sanitizedContent }} />
  );
}

• This example uses the DOMPurify library (replace with your preferred sanitizer) to remove potential XSS vulnerabilities from the htmlContent.
• The sanitized content is then injected into the DOM using dangerouslySetInnerHTML.

Important Note:

• Sanitization is crucial! Never use dangerouslySetInnerHTML with untrusted content without proper sanitization.
• Explore libraries like DOMPurify or others that meet your specific sanitization needs.

These examples demonstrate how to achieve similar results without raw HTML:

a) Component Composition:

import React from 'react';

function BoldText(props) {
  return <b>{props.children}</b>; // Reusable bold text component
}

function MyComponent() {
  return (
    <div>
      <BoldText>This is bold text</BoldText> using component composition.
    </div>
  );
}

• This example creates a reusable BoldText component to handle bold formatting.
• This promotes separation of concerns and keeps your code cleaner.

b) Controlled Components:

import React, { useState } from 'react';

function MyComponent() {
  const [userInput, setUserInput] = useState(''); // State for user input

  const handleChange = (event) => {
    setUserInput(event.target.value);
  };

  return (
    <div>
      <input type="text" value={userInput} onChange={handleChange} />
      <p>You entered: {userInput}</p> // Display user input without rendering as HTML
    </div>
  );
}

• This example uses a controlled component (input) to manage user input in a state variable (userInput).
• The input value is displayed as plain text, preventing XSS vulnerabilities.

• For simple, trusted content: Use Unicode and UTF-8 encoding.
• For untrusted content (with extreme caution): Sanitize thoroughly with dangerouslySetInnerHTML.
• Generally: Prioritize component composition and controlled components for better security and maintainability.

1. Libraries for Parsing and Transforming HTML:

   • These libraries allow you to parse the HTML string into a safer representation, like a JavaScript object structure, before rendering it within your components. This provides more control over the output and helps prevent XSS vulnerabilities.
   • Popular options include:
     • react-html-parser (parses HTML into React elements)
     • dompurify (mentioned earlier, can also be used for parsing and transforming)
   • Example using react-html-parser (remember to install the library):

   import React from 'react';
   import parse from 'react-html-parser';
   
   function MyComponent() {
     const htmlContent = '<b>This is bold text</b> with a <span style="color: red;">red span</span>.';
     const parsedContent = parse(htmlContent); // Parse HTML into React elements
     return (
       <div>{parsedContent}</div>
     );
   }
   

   • The parse function from react-html-parser converts the HTML string into React elements.
   • This allows you to render the content safely while still preserving some formatting.

2. Markdown Libraries:

   • If your content is primarily text-based with basic formatting needs, consider using a Markdown library. Markdown provides a simpler and safer way to format text compared to raw HTML.
   • Popular options include:
     • marked
     • react-markdown

   import React from 'react';
   import ReactMarkdown from 'react-markdown';
   
   function MyComponent() {
     const markdownContent = 'This is **bold text** with a [link](https://www.example.com).';
     return (
       <div>
         <ReactMarkdown>{markdownContent}</ReactMarkdown>
       </div>
     );
   }
   

   • The ReactMarkdown component parses the Markdown content and renders it as HTML elements within your React application.
   • This provides a safe and controlled way to format text with features like bold, italics, and links.