Violentmonkey

Ever wished you could tweak websites to perfectly suit your needs, adding features, removing annoyances, or even completely transforming their behavior? As someone who’s spent over 5 years deeply entrenched in JavaScript, I've found that one of the most empowering tools for this kind of web customization is a userscript manager. And among the various options out there, Violentmonkey stands out as a robust, flexible, and incredibly developer-friendly choice.

Violentmonkey isn't just another browser extension; it's a gateway to a world where you dictate how the web looks and feels for you. It allows you to inject custom JavaScript, CSS, and even HTML into virtually any webpage, turning passive browsing into an active, personalized experience. From automating mundane tasks to enhancing user interfaces, the possibilities are genuinely limitless when you harness its power.

In this post, I want to share my insights and some crucial developer tips gleaned from years of working with userscripts. We’ll dive into common challenges, how to sidestep frustrating bugs, and even touch upon broader JavaScript advancements that empower these tiny, yet mighty, scripts.

At its core, Violentmonkey is an open-source browser extension that manages userscripts. These scripts are essentially small JavaScript programs that run in the context of a webpage after it loads. Think of it as having a miniature developer console running automatically on specific sites, executing your custom code. The beauty of Violentmonkey lies in its simplicity for installation and its powerful API for script creation.

I remember my first foray into userscripting years ago. I was constantly frustrated by a particular forum's outdated UI and lack of a dark mode. With Violentmonkey, I crafted a script that not only restyled the entire site with custom CSS but also added quick-reply buttons and enhanced navigation using JavaScript. It was a game-changer for my productivity, proving that even small tweaks could have a huge impact. This experience cemented my belief in the power of client-side customization.

---

Navigating Common Userscript Challenges

While Violentmonkey is fantastic, working with userscripts isn't without its quirks. One common hurdle I've encountered, and seen many others struggle with, is related to script execution control. Specifically, the issue where a Violentmonkey userscript cannot get @exclude to work for specific URL. This often happens when developers misinterpret how @match, @include, and @exclude directives interact.

The @match directive is generally the most robust and recommended for specifying URLs. However, when you need fine-grained control, @include and @exclude come into play. A common mistake is having an overly broad @match or @include that overrides a more specific @exclude. Remember, @exclude takes precedence over @include, but the order and specificity of your directives matter. If your @match is too general, it might ignore a later @exclude. Always test your match patterns thoroughly!

// @match        https://example.com/*
// @exclude      https://example.com/admin/*
// @exclude      https://example.com/settings*
// My script will run on all pages of example.com EXCEPT admin and settings pages.

Another classic pitfall for JavaScript developers, particularly when dealing with data fetched from external sources within a userscript, is the dreaded Uncaught TypeError: query.data?.map is not a function. This error instantly tells me two things: first, that query.data is likely null or undefined, and second, that whatever query.data is, it's not an array or an array-like object that has a .map() method. This often stems from an API call failing, returning an unexpected data structure, or simply taking too long to resolve, leading to your script trying to process non-existent data.

Warning: Always validate data received from external sources. Assume it might be missing or malformed.

fetch('https://api.example.com/data')
  .then(response => response.json())
  .then(query => {
    if (query && Array.isArray(query.data)) {
      query.data.map(item => {
        // Process item
        console.log(item);
      });
    } else {
      console.error('Expected an array for query.data, but received:', query);
    }
  })
  .catch(error => console.error('Error fetching data:', error));

This type of error highlights the importance of robust coding best practices, especially defensive programming. Always check for the existence and type of data before attempting to operate on it. Using optional chaining (?.) is a good start, but it doesn't solve the problem if the final property isn't an array. Combine it with `typeof` checks or `Array.isArray()` for true resilience.

---

Beyond Basic Tweaks: Advanced Userscripting and JavaScript's Evolution

Userscripts aren't just for simple DOM manipulation. With Violentmonkey, you can leverage the full power of modern JavaScript. This includes asynchronous operations, working with Web APIs, and even integrating with cutting-edge proposals. For instance, consider the incredible work being done with Temporal: The 9-Year Journey to Fix Time in JavaScript. While it's a new API for handling dates and times more robustly, a sophisticated userscript could hypothetically use it to display localized, time-zone-aware event times on a global website, fixing a common pain point for users.

In my own projects, I've often used Violentmonkey to inject complex React or Vue applications into existing pages, essentially building mini-apps that run on top of an existing site. This is particularly useful when you need to add significant functionality without having direct control over the server-side code. It requires careful handling of shadow DOM or unique element IDs to avoid conflicts, but the results can be incredibly powerful.

"The real power of userscripts comes from their ability to fill the gaps left by a website's original design, making the web truly yours."

Here are a few developer tips I swear by when writing userscripts:

1. Scope Your Scripts Carefully: Use @match and @exclude directives precisely. Overly broad scripts can lead to performance issues or unexpected behavior on pages you didn't intend to target.
2. Isolate Your Code: Wrap your entire script in an Immediately Invoked Function Expression (IIFE) (function() { /* your code */ })(); to prevent variable collisions with the host page's JavaScript.
3. Use Modern JavaScript: Violentmonkey supports modern ECMAScript features. Don't be afraid to use async/await, arrow functions, and const/let.
4. Debug with Browser DevTools: Even though it's a userscript, you can debug it like any other script. Set breakpoints, inspect variables, and use console.log() liberally. The "Sources" tab is your best friend.
5. Handle DOM Changes: Websites are dynamic. If you're modifying elements that might be removed or re-added, use MutationObserver to react to DOM changes, rather than just running your script once on page load. I once spent an entire afternoon wondering why my script stopped working after a user interacted with a modal, only to realize the modal was dynamically re-rendered, taking my injected elements with it! A MutationObserver would have saved me hours.

Tip: Always check the Violentmonkey documentation for specific API functions like GM_xmlHttpRequest for making cross-origin requests, which are essential for many userscript functionalities.

Conclusion

Violentmonkey offers an unparalleled level of control over your browsing experience. Whether you're a seasoned JavaScript developer looking to automate your workflow or someone just starting to explore web customization, it provides a powerful and flexible platform. By understanding its directives, embracing coding best practices, and staying aware of common pitfalls like incorrect @exclude patterns or unexpected data types leading to TypeErrors, you can unlock a truly personalized web.

The web is constantly evolving, and with tools like Violentmonkey, you have the power to evolve with it, bending it to your will rather than just passively consuming it. So go ahead, write that script, fix that annoyance, and make the internet a better place—one custom tweak at a time!

What is the primary difference between Violentmonkey and Tampermonkey?

In my experience, both Violentmonkey and Tampermonkey offer very similar core functionalities as userscript managers. The main differences often come down to user interface preferences, specific feature implementations, and performance. Violentmonkey tends to be praised for its lighter footprint and open-source nature, while Tampermonkey has a slightly larger user base and can sometimes offer more frequent updates or experimental features. I've personally found Violentmonkey's UI to be a bit cleaner and more straightforward, which suits my development style.

How can I ensure my userscript runs only on HTTPS pages?

To ensure your userscript runs exclusively on HTTPS pages, you should explicitly specify https:// in your @match or @include directives. For example, instead of // @match *://example.com/*, use // @match https://example.com/*. This tightens the scope and prevents accidental execution on insecure connections. I always make this a habit for any script handling sensitive data or making external requests, following good security coding best practices.

What are the common causes of a userscript not running?

From my debugging sessions, the most common reasons a userscript might not run include incorrect @match or @include directives (leading to the script not being injected into the desired page), a syntax error in the script itself (which you'll usually see in the browser's console), or the script being disabled in the Violentmonkey extension's dashboard. I always start by checking the browser console for errors and then reviewing the script's metadata block for correct URL matching, as these catch about 90% of the issues.

Source:
www.siwane.xyz
A special thanks to GEMINI and Jamal El Hizazi.