A Complete Guide to Script Tag Types in HTML

A Complete Guide to Script Tag Types in HTML

Asgarali Dekavadiya Asgarali Dekavadiya

Asgarali Dekavadiya

Remote Frontend Developer | Expert in Vue.js, jQuery, Javascript, and Responsive Design

发布日期: 2025年2月24日
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Introduction

The <script> tag is a fundamental element in HTML used to embed JavaScript code within a webpage. However, there are multiple types of script tags, each serving different purposes. Understanding these script tag types can help you optimize performance, improve SEO, and enhance user experience.

In this article, we’ll explore all script tag types, their attributes, and best practices for their usage.

1. Basic <script> Tag

The most common <script> tag allows you to add JavaScript either inside an HTML file (inline script) or externally through a separate file.

Inline JavaScript

<script>
    console.log('Hello, World!');
</script>

Inline scripts are useful for small JavaScript snippets but are not recommended for large projects due to maintenance and performance concerns.

External JavaScript

<script src="script.js"></script>

Using an external JavaScript file helps keep HTML cleaner and improves maintainability.

2. async and defer Attributes

When including an external script, you can control when it loads using async and defer.

async (Asynchronous Loading)

<script src="script.js" async></script>

  • Loads the script in parallel with the page.
  • Executes immediately once loaded.
  • Can cause issues if scripts depend on one another.

defer (Deferred Execution)

<script src="script.js" defer></script>

  • Loads the script in parallel but waits until the DOM is fully loaded before executing.
  • Preserves script execution order.
  • Recommended for non-blocking scripts that modify the DOM.

AttributeLoadingExecutionasyncParallelImmediately after loadingdeferParallelAfter HTML is parsed

3. Module Scripts (type="module")

Module scripts allow JavaScript code to be imported and exported between files.

领英推荐

<script type="module">
    import { greet } from './module.js';
    greet();
</script>

  • Supports ES6 modules.
  • Automatically defers execution.
  • Runs in strict mode by default.

4. NoScript Fallback (<noscript>)

For users with JavaScript disabled, you can provide a fallback using <noscript>. 

<noscript>
    <p>Please enable JavaScript to view this content.</p>
</noscript>

This ensures a better user experience for those who have disabled JavaScript in their browsers.

5. Preloading and Prefetching Scripts

Using <link> to preload JavaScript files can improve performance. 

<link rel="preload" href="script.js" as="script">

This tells the browser to prioritize loading the script early.

6. Inline Event Handlers vs. External Event Listeners

Instead of inline event handlers like: 

<button onclick="alert('Clicked!')">Click Me</button>

Use external event listeners: 

<script>
    document.getElementById("myButton").addEventListener("click", function() {
        alert("Clicked!");
    });
</script>

This separates JavaScript logic from HTML, improving maintainability.

7. Best Practices for Script Optimization

  1. Use defer for scripts that manipulate the DOM.
  2. Minify JavaScript to reduce file size.
  3. Bundle and compress scripts to limit HTTP requests.
  4. Load scripts conditionally to improve performance.
  5. Use a CDN for faster script delivery.
  6. Keep scripts at the bottom of <body> if not using defer.
  7. Avoid inline scripts to enhance security and maintainability.

Conclusion

The <script> tag is essential for adding JavaScript to a webpage, but understanding the different types and attributes can greatly impact your website’s performance and SEO. By using best practices like defer, async, modules, and script preloading, you can ensure that your website loads efficiently and provides a smooth user experience.

Do you have any questions?

Drop your comments below, and let’s discuss!

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