Does it still make sense to use HTML comments on blocks of JavaScript?

HTML Comments for JavaScript Blocks: A Relic or a Relevant Practice?

Explore the historical context, current implications, and best practices for using HTML comments to encapsulate JavaScript code, and understand why modern development largely avoids it.

In the early days of the web, a common practice was to wrap JavaScript code within HTML comments (<!-- ... -->) inside <script> tags. This was primarily done to prevent older browsers, which didn't understand the <script> tag, from rendering the JavaScript code as plain text on the page. While browser technology has advanced significantly, the question occasionally arises: Does this practice still hold any relevance today, or is it a historical artifact best left in the past?

The Historical Context: Browser Compatibility

The primary motivation for using HTML comments around JavaScript was browser compatibility. Browsers that predated JavaScript support would simply ignore the <script> tags and display the content within them as regular text. By wrapping the JavaScript in HTML comments, these older browsers would treat the entire block as a comment, effectively hiding the code from the user's view. Modern browsers, on the other hand, are designed to correctly parse <script> tags and execute the JavaScript within, even if it's commented out with HTML comment syntax.

flowchart TD
    A[Browser Encounters Script Tag]
    A --> B{Is Browser Old (Pre-JS)?}
    B -->|Yes| C[Treats Script Content as Text]
    C --> D{Is Script Content HTML Commented?}
    D -->|Yes| E[Ignores Content (as comment)]
    D -->|No| F[Displays Script Content on Page]
    B -->|No| G[Treats Script Content as Code]
    G --> H{Is Script Content HTML Commented?}
    H -->|Yes| I[Executes Code (modern browser behavior)]
    H -->|No| I
    I[JavaScript Executed]

Browser behavior with HTML-commented JavaScript

Modern Implications and Best Practices

Today, all widely used browsers fully support JavaScript and the <script> tag. Consequently, the original reason for using HTML comments is entirely obsolete. In fact, continuing this practice can introduce subtle issues or simply add unnecessary clutter to your code. Modern JavaScript development emphasizes clean, readable, and maintainable code. Encapsulating JavaScript within HTML comments goes against these principles.

<!-- Old, deprecated practice -->
<script type="text/javascript">
<!--
    console.log("This is JavaScript wrapped in HTML comments.");
//-->
</script>

<!-- Modern, recommended practice -->
<script>
    console.log("This is modern JavaScript.");
</script>

Comparison of old and modern JavaScript embedding practices

The //--> and <!-- within <script>

You might also encounter the //--> and <!-- syntax within the <script> block itself. The // is a JavaScript single-line comment, and the --> is the closing HTML comment tag. The // effectively comments out the --> for JavaScript engines, preventing a syntax error. Similarly, the <!-- is often preceded by // to comment it out for JavaScript. This convoluted syntax further highlights the hacky nature of the original workaround and its irrelevance today.

<script type="text/javascript">
<!--
    // Your JavaScript code here
    var message = "Hello, World!";
    alert(message);
//-->
</script>

Example of the full historical HTML comment and JavaScript comment combination

In conclusion, the use of HTML comments to hide JavaScript blocks is a historical artifact. It served a purpose in a bygone era of web development but has no place in modern, standards-compliant web applications. Always strive for clean, semantic HTML and JavaScript, keeping your code readable and maintainable for current and future developers.