tshy

tshy - TypeScript HYbridizer

Hybrid (CommonJS/ESM) TypeScript node package builder.

This tool manages the exports in your package.json file, and builds your TypeScript program using tsc 5.2 in both ESM and CJS modes.

USAGE

Install tshy:

npm i -D tshy

Put this in your package.json to use it with the default configs:

{
  "files": ["dist"],
  "scripts": {
    "prepare": "tshy"
  }
}

Put your source code in ./src.

The built files will end up in ./dist/esm (ESM) and ./dist/commonjs (CommonJS).

Your exports will be edited to reflect the correct module entry points.

Configuration

Mostly, this is opinionated convention, and so there is very little to configure.

Source must be in ./src. Builds are in ./dist/cjs for CommonJS and ./dist/mjs for ESM.

There is very little configuration for this. The only thing to decide is the exported paths. If you have a ./index.ts file, then that will be listed as the main "." export by default.

You can set other entry points by putting this in your package.json file:

{
  "tshy": {
    "exports": {
      "./foo": "./src/foo.ts",
      "./bar": "./src/bar.ts",
      ".": "./src/something-other-than-index.ts",
      "./package.json": "./package.json"
    }
  }
}

Any exports pointing to files in ./src will be updated to their appropriate build target locations, like:

{
  "exports": {
    "./foo": {
      "import": {
        "types": "./dist/mjs/foo.d.ts",
        "default": "./dist/mjs/foo.js"
      },
      "require": {
        "types": "./dist/cjs/foo.d.ts",
        "default": "./dist/cjs/foo.js"
      }
    }
  }
}

Any exports that are not within ./src will not be built, and can be either a string, or a { import, require, types } object:

{
  "exports": {
    "./package.json": "./package.json"
    "./thing": {
      "import": "./lib/thing.mjs",
      "require": "./lib/thing.cjs",
      "types": "./lib/thing.d.ts"
    }
  }
}

Selecting Dialects

You can tell tshy which dialect you're building for by setting the dialects config to an array of strings:

{
  "tshy": {
    "dialects": ["esm", "commonjs"]
  }
}

The default is ["esm", "commonjs"] (ie, both of them). If you set it to just one, then only that dialect will be built and exported.

CommonJS Dialect Polyfills

Sometimes you have to do something in different ways depending on the JS dialect in use. For example, maybe you have to use import.meta.url in ESM, but polyfill with pathToFileURL(__filename) in CommonJS.

To do this, create a polyfill file with the CommonJS code in <name>-cjs.cts. (The cts extension matters.)

// src/source-dir-cjs.cts
//     ^^^^^^^^^^--------- matching name
//               ^^^^----- "-cts" tag
//                   ^^^^- ".cts" filename suffix
// this one has a -cjs.cts suffix, so it will override the
// module at src/source-dir.ts in the CJS build,
// and be excluded from the esm build.
import { pathToFileURL } from 'node:url'
//@ts-ignore - Have to ignore because TSC thinks this is ESM
export const sourceDir = pathToFileURL(__dirname)

Then put the "real" ESM code in <name>.ts (not .mts!)

// src/source-dir.ts
// This is the ESM version of the module
export const sourceDir = new URL('.', import.meta.url)

Then in your code, you can just import { sourceDir } from './source-dir.js' and it'll work in both dialects.

.cts and .mts files

Files named *.mts will be excluded from the CommonJS build.

Files named *.cts will be excluded from the ESM build.

If you need to do something one way for CJS and another way for ESM, use the "Dialect Switching" trick, with the ESM code living in src/<whatever>.ts and the CommonJS polyfill living in src/<whatever>-cjs.cts.

Atomic Builds

Code is built in ./.tshy-build-tmp and then copied over only if the build succeeds. This makes it work in monorepo cases where you may have packages that depend on one another and are all being built in parallel (as long as they've been built one time, of course).

Exports Management

The exports field in your package.json file will be updated based on the tshy.exports configuration, as described above.

If you don't provide that config, then the default is:

{
  "tshy": {
    "exports": {
      ".": "./src/index.ts",
      "./package.json": "./package.json"
    }
  }
}

Package #imports

Using the imports field in package.json is not currently supported, because this looks at the nearest package.json to get local imports, and the package.json files placed in dist/{cjs,mjs} can't have local imports outside of their folders.

There's a way it could theoretically be done, but it's a bit complicated. A future version may support this.

TSConfigs

Put whatever configuration you want in tsconfig.json, with the following caveats:

• include - will be overridden based on build, best omitted
• exclude - will be overridden based on build, best omitted
• compilerOptions:
  • outDir - will be overridden based on build, best omitted
  • rootDir - will be set to ./src in the build, can only cause annoying errors otherwise.
  • target - will be set to es2022
  • module - will be set to NodeNext
  • moduleResolution - will be set to NodeNext

If you don't have a tsconfig.json file, then one will be provided for you.

Then the tsconfig.json file will be used as the default project for code hints in VSCode/nvim, your tests, etc.

src/package.json

As of TypeScript 5.2, the only way to emit JavaScript to ESM or CJS, and also import packages using node-style "exports"-aware module resolution, is to set the type field in the package.json file closest to the TypeScript source code.

During the build, tshy will create a file at src/package.json for this purpose, and then delete it afterwards. If that file exists and wasn't put there by tshy, then it will be destroyed.