🔎 Focus: Site Speed
🔴 Impact: High
🟠 Difficulty: High-Medium

For a long time, third-party scripts didn’t feel like a real problem.

Analytics, tag managers, chat widgets, A/B testing tools - they all slowed things down a bit, but:

So, performance optimization often stopped at image compression and a CDN. As long as nothing was obviously broken, it was good enough.

Your website was fast enough.

But modern websites don’t load one or two scripts anymore. They load dozens. And almost all of them compete for the most critical resource in the browser: the main thread.

At that point, “fast enough” starts becoming slow.

A lot of performance issues today come from:

All of these scripts:

In practice, it’s not network speed that hurts you - it’s Javascript execution.

🧑‍💻 Technical Note: The browser can download many files in parallel, but it can only execute JavaScript on the main thread, one task at a time.

This means every third-party script:

The result:

In the case below third-party scripts block the thread for over 6 seconds which is a long time.

Most third-party scripts already use async or defer.

And yet… performance is still bad.

Why?

Because async and defer only change when scripts execute - not where.

They still:

🧑‍💻 Reality check:
Even a deferred script can cause long tasks and jank if it’s heavy enough.

This is the ceiling of traditional script optimization.

Partytown changes the execution model entirely.

Instead of running third-party scripts on the main thread, it runs them inside a Web Worker.

What does that give you:

In short:
Your page loads while third-party scripts run in the background.

🧑‍💻 How it works (simplified):
Partytown proxies browser APIs so third-party scripts believe they are running normally, while actually executing off the main thread.

This makes it ideal for:

Scripts still work → They just stop blocking everything else.

Moving third-party scripts to Partytown typically results in:

The biggest gains happen on:

🧑‍💻 Important:
Partytown doesn’t make scripts faster.
It makes them less disruptive.

That’s often the difference between a page feeling sluggish and feeling instant.

Partytown is powerful, but it’s not universal.

1. Use it only for third-party scripts
Never move critical rendering or business logic.

2. Start with analytics and marketing tools
These scripts are the most expensive and least critical for rendering.

3. Test events and tracking carefully
Some third-party tools rely on synchronous execution, and moving them to a web worker disrupts the event handling.

4. Monitor performance before and after
Track TBT, INP, and long tasks.

🧑‍💻 Rule of thumb:
If the page can render without a third-party script, it probably belongs in Partytown.

At this point, the goal should be clear:
protect the main thread and let content render first.

Partytown is not a generic performance tool - it solves a very specific problem:
third-party scripts stealing time from rendering and interactivity.

The table below maps common performance problems directly to how Partytown addresses them.

Many modern websites aren’t slow only because of images or servers.
They’re slow because too much JavaScript fights for the main thread.

Partytown doesn’t remove third-party scripts - it puts them in their place.

If you care about site speed, smooth interactions, and real-world performance, optimizing third-party scripts is no longer optional.

And Partytown is one of the cleanest ways to do it.

Until next time 👋

Patryk