Code Splitting and Bundle Size
On modern interactive sites, the JavaScript can grow into one enormous file that every visitor must download before the page works, even if they only use a fraction of it. Code splitting breaks that bundle into smaller pieces loaded only when needed.
The result is a lighter initial download and a faster, more responsive first experience.
Why Size Matters
Every extra kilobyte of JavaScript has to be downloaded, parsed and run before parts of the page respond. Keeping bundles small therefore improves not just download time but how quickly the page reacts to taps and clicks, especially on modest mobile devices.
How We Keep Bundles Small
Keeping JavaScript lean is an ongoing discipline rather than a one-off task. As features are added, we watch the bundle size so the site does not slowly grow heavier over time.
- Audit which libraries are actually used.
- Replace heavy dependencies with lighter ones.
- Split code so pages load only what they need.
- Track bundle size as part of each release.
What You Will Notice
For visitors, the benefit of code splitting is a page that becomes usable sooner, especially on the first visit and on mobile. They never see the technique itself — only a snappier experience.
- The first page loads faster because it ships less code.
- Heavier features load only when someone uses them.
- Repeat visits are quicker as shared code is cached.
- The site scales better as features are added over time.
The Problem with Big Bundles
A large bundle takes longer to download, parse and run. On a phone over a mobile connection, that delay can be the difference between a snappy page and a frustrating one.
How Splitting Helps
- The home page only loads the code the home page needs.
- Features like a checkout load their code when a visitor reaches them.
- Shared code is cached and reused across pages.
Keeping Bundles Lean
- Remove libraries that are no longer used.
- Choose lightweight alternatives where they exist.
- Split code by route and by feature so nothing loads before it is needed.
If you need a hand with any of this, your Progressive Robot delivery team is ready to help. Raise a ticket from the Support area of your client portal or speak to your account manager and we will guide you through the next steps.