I write stuff in TypeScript and used Tape as a test runner. After converting my project to use ECMAScript modules (ESM), tape stopped working, causing quite a bit of headache.

2023-09-27 How to use Tape with TypeScript and ESM.md

2023-09-27 How to use Tape with TypeScript and ESM

I write stuff in TypeScript and used Tape as a test runner. After converting my project to use ECMAScript modules (ESM), tape stopped working, causing quite a bit of headache.

Goals

• Write tests in TypeScript. Tests live next to source files.
• Do not compile tests to the dist directory.
• Use ts-node to transpile tests on the fly and use tape as the test runner.

What doesn't work anymore

• Use ts-node tape to run stuff. Results in various errors, because tape isn't a true ESM package (I think).

Structure

I converted my project to ESM based on Sindre Sorhus' guide.

This is an excerpt of my package.json:

{
    //...
    "type": "module",
    "scripts": {
        "test": "node --loader ts-node/esm node_modules/tape/bin/tape 'src/**/*.spec.ts' | tap-diff",
    }
    // ...
}

ts-config.json:

{
    "compilerOptions": {
        "moduleResolution": "node16",
        "module": "node16",
        "target": "es2017",
        "declaration": true,
        "outDir": "./dist",
        "lib": ["dom", "es2017"],
        "baseUrl": "./src",
    },
    "include": ["./src/**/*.ts"],
    "exclude": ["node_modules", "dist", "src/**/test"],

    "ts-node": {
        "transpileOnly": true,
        "files": true,
        "experimentalResolver": true
    }
}

Unfortunately, it doesn't work right out of the box:

SyntaxError: Cannot use import statement outside a module
    at internalCompileFunction (node:internal/vm:73:18)
    at wrapSafe (node:internal/modules/cjs/loader:1153:20)
    at Module._compile (node:internal/modules/cjs/loader:1205:27)
    at Module._extensions..js (node:internal/modules/cjs/loader:1295:10)
    at Module.load (node:internal/modules/cjs/loader:1091:32)
    at Module._load (node:internal/modules/cjs/loader:938:12)
    at Module.require (node:internal/modules/cjs/loader:1115:19)
    at require (node:internal/modules/helpers:130:18)
    at importOrRequire (./node_modules/tape/bin/import-or-require.js:14:2)

The culprit is tape. It doesn't like the .ts-extension. I had to patch tape this way:

Edit node_modules/tape/bin/import-or-require.js line 11 (in tape 5.7.0) and tell tape to also load .ts-files. Because it's just the filename. It'll be transpiled on the fly via the ts-node loader.

if (ext === '.mjs' || (ext === '.js' && getPackageType.sync(file) === 'module') || (ext === '.ts' && getPackageType.sync(file) === 'module')) {

After that, it runs flawlessly. Don't like editing files in node_modules? I didn't either, but since I learned about the extremely simple patch-package, I use it quite often to reliably change small errors. Read more about it here and here.