Overriding `tsconfig.json` for ts-node in mocha

Question

Is it possible to override which tsconfig.json ts-node uses when called from mocha?

My main tsconfig.json contains "module": "es2015", but I want to use "module": "commonjs" for ts-node only.

I tried this

mocha --compilers ts:ts-node/register,tsx:ts-node/register \
    --compilerOptions '{"module":"commonjs"}' \
    --require ts-node/register test/**/*.spec.ts*

but it did not work:

SyntaxError: Unexpected token import
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:387:25)
    at Module.m._compile (/usr/lib/node_modules/ts-node/src/index.ts:406:23)
    at Module._extensions..js (module.js:422:10)
    at Object.require.extensions.(anonymous function) [as .tsx] (/usr/lib/node_modules/ts-node/src/index.ts:409:12)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Module.require (module.js:367:17)
    at require (internal/module.js:16:19)
    at /usr/lib/node_modules/mocha/lib/mocha.js:222:27
    at Array.forEach (native)
    at Mocha.loadFiles (/usr/lib/node_modules/mocha/lib/mocha.js:219:14)
    at Mocha.run (/usr/lib/node_modules/mocha/lib/mocha.js:487:10)
    at Object.<anonymous> (/usr/lib/node_modules/mocha/bin/_mocha:458:18)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at startup (node.js:146:18)
    at node.js:404:3

Answer 1

--compilerOptions wont' work.

What you need to do is customize how you register ts-node. My case was a little bit different from yours, I wanted it to use test/tsconfig.json, which contained settings needed by my test code. If I just used --require ts-node/register, it was using a default configuration that did not contain the settings needed to run my tests.

What I did was:

1. Create a file test/tshook.js. It contains:

   require("ts-node").register({
     project: "test/tsconfig.json",
   });
   

2. I edited my test/mocha.opts to have:

   --require test/tshook.js
   test/**/*.ts
   

This should will pass the desired setting to ts-node:

require("ts-node").register({
  compilerOptions: {
    module: "commonjs",
  },
});

Answer 2

You need to set the configuration through the TS_NODE_COMPILER_OPTIONS environment variable

Example code on an unix machine:

TS_NODE_COMPILER_OPTIONS='{"module":"commonjs"}' \
mocha --require ts-node/register 'test/**/*.spec.{ts,tsx}'

---

Explanation extracted from the repository documentation

---

CLI and Programmatic Options

Environment variable denoted in parentheses.

• --typeCheck Enable type checking for TypeScript (TS_NODE_TYPE_CHECK)
• --cacheDirectory Configure the output file cache directory (TS_NODE_CACHE_DIRECTORY)
• -I, --ignore [pattern] Override the path patterns to skip compilation (TS_NODE_IGNORE)
• -P, --project [path] Path to TypeScript JSON project file (TS_NODE_PROJECT)
• -C, --compiler [name] Specify a custom TypeScript compiler (TS_NODE_COMPILER)
• -D, --ignoreDiagnostics [code] Ignore TypeScript warnings by diagnostic code (TS_NODE_IGNORE_DIAGNOSTICS)
• -O, --compilerOptions [opts] JSON object to merge with compiler options (TS_NODE_COMPILER_OPTIONS)
• --no-cache Disable the local TypeScript Node cache (TS_NODE_CACHE)
• --skip-project Skip project config resolution and loading (TS_NODE_SKIP_PROJECT)
• --skip-ignore Skip ignore checks (TS_NODE_SKIP_IGNORE)

Answer 3

In package.json - scripts section:

"test": "TS_NODE_PROJECT=src mocha"

picks up my tsconfig.json in the src directory of my project, overriding the default tsconfig.json.

OP can achieve same by using test instead of src