Errors / JavaScript errors

ChunkLoadError: Loading chunk … failed

Part of the site's code could not be downloaded, usually because the site changed since the page was opened.

A route or a feature does not load until the visitor refreshes.

Why it happens

• The webpack or Next.js version of the same problem: a deploy removed the chunk an open tab still asks for.
• A chunk URL answering HTML (a 404 page) instead of JavaScript.
• A flaky connection timing out on one of many small files.

How to fix it

1. Keep old build assets for some time after a deploy; with Next.js, a deployment ID or skew protection keeps a tab on its own version.
2. Catch the error at the route level and reload the page once.
3. Check the chunk URL in the failed requests: a 404 or HTML means a deploy, a timeout means the network.

Whose problem it is

Usually the site's own code or settings.

Often seen with

• Failed to fetch dynamically imported moduleThe site was updated while the visitor had it open, and the part they clicked on no longer exists.