Compile time errors being suppressed when using esm

[Stono]

I really struggled to think of the correct title for this, so please edit it as required. I went down a rabbithole today whilst moving one of our apps to esm, as it was failing to start (with ts-node) due to the following node error:

❯ node --experimental-specifier-resolution=node --loader ts-node/esm lib/index.ts
node:internal/modules/run_main:115
    triggerUncaughtException(
    ^
[Object: null prototype] {
  [Symbol(nodejs.util.inspect.custom)]: [Function: [nodejs.util.inspect.custom]]
}

Node.js v22.5.1

Doesn't really give away much. It turned out however that the root caused we missed a return type on a promise eg Promise needed to be Promise<void>. This error was visible if you did a tsc, but ts-node was giving this output.

After gradually chipping away at the code to make a minimal example; i managed to reproduce it with a really simple bit of code that doesn't even technically have an error in it.

Assuming your code is in ./lib, create ./lib/index.ts:

import { SomeServer } from './server.js'

const webServer = new SomeServer()

and ./lib/server.ts:

export class SomeServer {}

If you try and start this; you'll get the error. The only thing "wrong" with this code is the fact that webServer is an unused variable. If i add console.log(webServer), eg:

import { SomeServer } from './server.js'

const webServer = new SomeServer()
console.log(webServer)

Then all is well:

❯ node --experimental-specifier-resolution=node --loader ts-node/esm lib/index.ts

SomeServer {}

Specifications

• versions:

  ❯ ./node_modules/.bin/ts-node -vv
  ts-node v10.9.2
  node v22.5.1
  compiler v5.3.3

• tsconfig.json:

  {
  "compilerOptions": {
  "lib": ["ES2022", "DOM"],
  "module": "ES2022",
  "target": "ES2022",
  "rootDir": "./",
  "outDir": "./built",
  "baseUrl": "./",
  "allowJs": false,
  "checkJs": false,
  "alwaysStrict": true,
  "noImplicitAny": true,
  "noImplicitThis": true,
  "strictNullChecks": true,
  "strictFunctionTypes": true,
  "strictPropertyInitialization": true,
  "noEmitOnError": false,
  "sourceMap": false,
  "declaration": false,
  "strictBindCallApply": true,
  "noImplicitOverride": true,
  "noUncheckedIndexedAccess": true,
  "incremental": false,
  "skipDefaultLibCheck": true,
  "experimentalDecorators": true,
  "noUnusedLocals": true,
  "esModuleInterop": true,
  "moduleResolution": "node",
  "emitDecoratorMetadata": true,
  "allowSyntheticDefaultImports": true,
  "forceConsistentCasingInFileNames": true,
  "noFallthroughCasesInSwitch": true
  },
  "include": ["lib/**/*.ts", "test/**/*.ts"],
  "exclude": ["node_modules/**/*"]
  }

• Operating system and version: Mac