ts-node with tsconfig-paths won't work when using esm

Question

I couldn't figure out why ts-node isn't resolving the alias when esm is enabled

I made a tiny project trying to isolate the issue as much as possible

package.json

{
  "type": "module"
}

tsconfig.json

{
  "compilerOptions": {
    "module": "es2020",                                
    "baseUrl": "./",                                  
    "paths": {
      "$lib/*": [
        "src/lib/*"
      ]
    },
  },
  "ts-node": {
    "esm": true
  }
}

test.ts

import { testFn } from "$lib/module"

testFn()

lib/module.ts

export function testFn () {
  console.log("Test function")
}

command

ts-node -r tsconfig-paths/register src/test.ts

Here's a minimal repo

@DDana Check the first line in my question, I linked to a solution — unloco, Apr 12 '22 at 12:02
I tried it but unfortunately did not succeed. I wrote a comment there. If you can unblock me would really appreciate it https://github.com/TypeStrong/ts-node/discussions/1450#discussioncomment-2560012 — DDana, Apr 13 '22 at 14:11
Just putting here OPs own answer [https://github.com/TypeStrong/ts-node/discussions/1450#discussioncomment-1806115](https://github.com/TypeStrong/ts-node/discussions/1450#discussioncomment-1806115) — Preda7or, Apr 24 '22 at 16:55
@Preda7or If you'd like to summarize or explain the solution, I will accept it as the solution. Cheers — unloco, Apr 24 '22 at 19:24

score 6 · Accepted Answer · answered Feb 02 '23 at 03:14

Solution from: https://github.com/TypeStrong/ts-node/discussions/1450#discussion-3563207

At the moment, the ESM loader does not handle TypeScript path mappings. To make it work you can use the following custom loader:

// loader.js
import {
  resolve as resolveTs,
  getFormat,
  transformSource,
} from "ts-node/esm";
import * as tsConfigPaths from "tsconfig-paths"

export { getFormat, transformSource };

const { absoluteBaseUrl, paths } = tsConfigPaths.loadConfig()
const matchPath = tsConfigPaths.createMatchPath(absoluteBaseUrl, paths)

export function resolve(specifier, context, defaultResolver) {
  const mappedSpecifier = matchPath(specifier)
  if (mappedSpecifier) {
    specifier = `${mappedSpecifier}.js`
  }
  return resolveTs(specifier, context, defaultResolver);
}

Then use the loader with: node --loader loader.js index.ts

Caveat: This only works for module specifiers without an extension. For example, import /foo/bar works, but import /foo/bar.js and import /foo/bar.ts do not.

Remember to install these packages as well:

"ts-node": "^10.9.1",
"tsconfig-paths": "^4.1.2",

don't forget to rexport `load` as well from `ts-node/esm` or else you'll get `TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"` — RyanDay, Mar 13 '23 at 05:28
Can we make this work with paths that end with `.js`? I suspect, this has something to do with `\`${mappedSpecifier}.js\`` — Parzh from Ukraine, Jun 20 '23 at 12:17

score 3 · Answer 2 · answered Jun 16 '23 at 13:26

3

I suggest to use esno esno src/test.ts

answered Jun 16 '23 at 13:26

David

1,094
9
9

score 1 · Answer 3 · answered Mar 15 '23 at 14:53

You can use @bleed-believer/path-alias to execute your ESM project (requires ts-node installed in your project):

npm i --save @bleed-believer/path-alias

To execute your source files with ts-node:

node --no-warnings --loader @bleed-believer/path-alias/esm ./src/test.ts

Assuming "outDir": "./dist", to execute your transpiled code directly with node (bypassing ts-node):

node --no-warnings --loader @bleed-believer/path-alias/esm ./dist/test.js

If you don't want to use the library to execute your transpiled project, you can use swc (this transpiler resolves the path aliases), or you can use tsc-alias after transpile your project with tsc.

ts-node with tsconfig-paths won't work when using esm

3 Answers3