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# A Practical Guide to Reducing Bundle Size


- **Date:** Friday, Jul 11, 2025
- **Time:** 09:00–09:30 (30 min)
- **Room:** Stage 10
- **Event:** World Congress 2025
- **Tags:** javascript, performance, typescript

## Recording

[Watch recording](https://www.wearedevelopers.com/videos/1439-a-practical-guide-to-reducing-bundle-size)

## Description

When it comes to bundle size, less really is more! But how do we ensure that our code can be effectively tree-shaken and minimised? 

There are common code patterns that break tree-shaking and prevent minification from doing much at all. Let me share practical insights from my experience optimising a component library that will help you do the same and shed the excess from your bundles.

The talk is split into 2 halves: tree-shaking / minification. 

Will explain tree-shaking then show coding patterns that prevent the bundler from being able to drop code. 
Will then cover sideEffects / pure code annotations.
Then how to test tree shaking is working and demo source-map-explorer.

Then will cover minification and how to optimise what the bundler can minify. #private variables unlock great savings but there are issues with downleveling for older build targets. 

The talk finishes with a quick overview of different build tools and the speed / size trade off. 

## Speaker

### [Stephen Cooper](https://www.wearedevelopers.com/@stephen-cooper)

Senior Developer at AG Grid


## Related talks at this congress

- [MVI: Minimum Viable Interface for React Components](https://www.wearedevelopers.com/events/world-congress-2025/sessions/909-mvi-minimum-viable) — Daniel Espino Garcia
- [Modular Secrets to Lightning-Fast Android Builds](https://www.wearedevelopers.com/events/world-congress-2025/sessions/834-modular-secrets-to) — Mohamed Gamal
- [The Future of React: A Deep Dive into Its Compiler and Auto Optimization](https://www.wearedevelopers.com/events/world-congress-2025/sessions/519-the-future-of-react) — Hammad Hassan
- [The Dependency Cookbook - Recipes for Micro Frontend success](https://www.wearedevelopers.com/events/world-congress-2025/sessions/645-the-dependency) — Lucas Braeschke, Stefan Bley