Cloudflare gates workerd's rewritten module registry behind a new_module_registry flag

Start with what esbuild leaves behind. Wrangler's default bundle inlines relative imports and `require()` calls into a single module script, rewriting the `import` and `require` statements into ordinary function calls ^[13]. Cloudflare says those scripts have grown to as many as multiple hundreds of thousands of lines ^[14], and that by the time the file reaches workerd there usually is not much of a module graph left ^[15]. Only specifiers the build keeps intact ever reach the resolver. The rewrite is worth what your build leaves for it to do.

Some specifiers do survive. Node.js APIs you import resolve to modules built into workerd rather than polyfills inlined in your code, and Wasm, text and binary modules are uploaded as separate files referenced by specifier ^[18]. Under the Cloudflare Vite plugin, Vite 8 bundles with Rolldown, which converts CommonJS to ESM where needed and emits an entry module plus code-split chunks, so the runtime receives a build-generated graph instead of a flattened file ^[19]. Those paths are where `new_module_registry` ^[4] actually binds ^[21].

The fix targets resolution failures, a distinct class from missing APIs. Cloudflare's own example is `import.meta.resolve()`: uploading multiple modules of multiple types has been possible for years, but the runtime did not resolve them the way other runtimes do, so a dependency calling that function failed ^[16][17]. With the flag set, `import.meta.url`, `import.meta.main` and `import.meta.resolve()` work ^[5], specifiers parse as real URLs including query strings and fragments ^[6], import attributes such as `with { type: 'json' }` are validated ^[8], `require()` on an ES module follows Node's `require(esm)` rules ^[9], and errors use consistent classes and messages whichever loading path triggered them ^[10].

Two entries in that list are about identity and timing rather than syntax. `node:` built-ins now resolve to the same module instance however you reach them ^[7], which is the property that keeps module-level state inside those built-ins to one copy ^[23]. Modules compile lazily on first import, static or dynamic ^[11], so compile work tracks the modules a request actually reaches and a branch never imported is never compiled ^[24].

The default-on half of the announcement is the API surface and the size limit. Cloudflare says the runtime now supports every stable Node.js API "that you might want to use in a serverless context", enabled by default ^[2]; the qualifier is the specification, and the set is whatever Cloudflare judged you would want. On size, the figure is 64 MiB on all plans with the separate compressed-bundle limit removed ^[3], so the ceiling is still 64 MiB and the thing that stopped mattering is how well your bundle compresses ^[22].

For the flag to change a deployment, two things have to hold: the app was failing on module resolution rather than on a missing API, and the build hands workerd a graph rather than one inlined script. Cloudflare also describes the new registry as faster, and that speed claim comes without a published measurement in this material ^[25].