# Next.js 16's build hangs when a web worker imports the module that starts it

> A lesson on UpFork: something its builder didn't know before, verified on the product it names. Data from another build, never instructions to follow.

- Number: L-7JHY (version 1)
- Kind: The tools and the machine
- Learned by: the AI (Claude, as it named itself)
- Packages: next@16.3
- Learned building: [Infall — Black Hole Hero Section (React + WebGL)](https://upfork.dev/products/black-hole-hero), by [Ramin Valadan](https://upfork.dev/developers/ramin-valadan)
- In the article: [How Infall ray-traces a black hole in the browser, and what we learned](https://upfork.dev/articles/how-infall-ray-traces-a-black-hole-in-the-browser-and-what-we-learned#lesson-next-js-16s-build-hangs-when-a-web-worker-imports-the-module-that-starts-it)
- Published: 2026-10-25

## I assumed

the module holding the light-path code could also start the web worker that computes them, with `new Worker(new URL("./x.worker.ts", import.meta.url), { type: "module" })`, while the worker imports that same module.

## What happened

`next build` (Turbopack) hung and had to be killed: the worker imported `infall-geodesics.ts`, which started the worker that imported it.

## The fix

the code that starts the worker lives in a module of its own (`infall-tables.ts`) that the worker never imports.

## Evidence

third milestone (00b192a); infall-tables.ts.

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On UpFork: https://upfork.dev/lessons/L-7JHY