terser-error-repro

Reproduction case for terser error.

Scripts

There are 3 yarn scripts available from anywhere in the project:

• yarn resolve:terser <desired terser version>
• yarn build-run:dev
• yarn build-run:prod

yarn resolve:terser <desired terser version>

Set the resolved terser version to <desired terser version>.

yarn build-run:dev

Build and then run a non-minified (i.e. no terser used) bundle of @repro/main-package with node. This is the control that the original code is not faulty, and that dependencies other than terser are not causing the error.

yarn build-run:prod

Build and then run a minified (by terser) bundle of @repro/main-package with node. If the error occurs, the build is successful, but the run ends in a ReferenceError: BaseClass is not defined runtime error.

Tested versions

The latest terser version that does not reproduce the error, is 5.15.0. From 5.15.1 to 5.17.4 the error does happen. Monorepo:

• Yarn 2 (berry) workspaces
• TypeScript, babel
• No build frameworks (lerna, nx, etc.)

Yarn 2 workspaces

This repo uses yarn plug-n-play.

Repo structure distinguishes

• main-package
• dependency-package

package.json in the top-level root directory:

{
  ...
  "private": true,
  "workspaces": [
    "main-package",
    "dependency-package"
  ],
  ...
}

Adding dependencies with their types

To add a dependency to a workspace, and automatically adding its types to devDependencies, run yarn add <dep-name> in that workspace. Yarn's TypeScript plugin finds the dependency's @types package, if it exists, and adds it to dev dependencies automatically.

Unplugging dependencies

Some packages may not work with yarn's plug-n-play mode. To make them work, unplugging those packages can help. This means that yarn will keep an unzipped version of a package, which comes closer to the node_modules linker. The base command is yarn unplug <package>.

• The option -R will also unplug the package's dependencies recursively.
• The option -A will unplug the package in every workspace that it's used in.

Notes on some dependencies.

• Some eslint-related packages need to be unplugged for eslint to work on Windows.

TypeScript

• Use for type checking.
• Target ESNext in all configurations (code and module format).
• JavaScript code generation.
• Use babel to transpile for a specific target. -> by using webpack

Scripts

{
  ...
  "scripts": {
    "type-check": "yarn run -T tsc --noEmit"
  },
  ...
}

yarn type-check

• Available from package main-package.
• Type-checks all project code used directly or indirectly by said package.