Internal Packages

An alternative approach to using internal dependencies in a TypeScript monorepo is the internal packages strategy, in which the package manifest entries point directly to TypeScript source files, to omit intermediate build steps. The approach is compatible with isolate-package and showcased in my example monorepo setup.

How It Works

1. The package to be deployed lists its internal dependencies as usual, but the package manifests of those dependencies point directly to the TypeScript source (and types).
2. You configure the bundler of your target package to include the source code for those internal packages in its output bundle. In the case of TSUP, you can use getInternalPackageNames for this: noExternal: await getInternalPackageNames()
3. When isolate runs, it does the same thing as always. It detects the internal packages, copies them to the isolate output folder and adjusts any links.
4. When deploying to Firebase, the cloud pipeline will treat the package manifest as usual, which installs the listed dependencies and any dependencies listed in the linked internal package manifests.

Steps 3 and 4 are no different from a traditional setup.

Note that the manifests for the internal packages in the output will still point to the TypeScript source files, but since the shared code was embedded in the bundle, they will never be referenced via import statements. So the manifest entry declarations are never used. The reason the packages are included in the isolated output is to instruct the package manager to install their dependencies.