Node.js: Cannot find module but the specified path exists

I am currently developing my own npm package and I created a separate project to download this package from npm for an independent test. The package is being developed in typescript and I have a main file with several additional module files. In my main file, I am importing all of the classes from the other modules, then exporting all of them under the main file. I don't know if this is good practice but when I run the main file on the test project, it says it can't find the module when the path it specifies exists in the working directory.

Code Snippets:

Main file:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

import { EventBus } from "./modules/eventbus/eventbus";
import { EventHandler } from "./modules/eventbus/eventhandler";
import { EventType } from "./modules/eventbus/eventtype";
import { Event } from "./modules/eventbus/event";
import { SemVer } from "./modules/semver";
export { SemVer, Event, EventBus, EventHandler, EventType };

<!-- end snippet -->

Error:

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/workspaces/epic-engine-testing/node_modules/epic-engine/lib/modules/eventbus/eventbus' imported from /workspaces/epic-engine-testing/node_modules/epic-engine/lib/index.js

Working directory:

Testing file:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

import { EventBus, EventHandler, EventType, Event } from "epic-engine";

class SomeType extends EventType {
    constructor() {
        super();
    }
}

const eventbus = new EventBus();
const handler = new EventHandler<SomeType>(eventbus, "type", () => {});
eventbus.createHandler(handler);
const event = new Event<SomeType>(eventbus, new SomeType(), "type");

<!-- end snippet -->

package.json:

{
  "devDependencies": {
    "@tsconfig/esm": "^1.0.2",
    "@types/jest": "^29.2.3",
    "jest": "^29.3.1",
    "ts-jest": "^29.0.3",
    "tslint": "^6.1.3",
    "typescript": "^4.9.3"
  },
  "name": "epic-engine",
  "description": "Pure TS engine developed by EpicPuppy613",
  "version": "0.1.0-dev.5",
  "main": "lib/index.js",
  "types": "lib/index.d.ts",
  "type": "module",
  "scripts": {
    "test": "jest --config jestconfig.json",
    "build": "tsc",
    "prepare": "npm run build",
    "lint": "tslint -p tsconfig.json",
    "prepublishOnly": "npm test && npm run lint",
    "preversion": "npm run lint",
    "version": "git add -A src",
    "postversion": "git push && git push --tags"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/EpicPuppy613/epic-engine.git"
  },
  "author": "EpicPuppy613",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/EpicPuppy613/epic-engine/issues"
  },
  "homepage": "https://github.com/EpicPuppy613/epic-engine#readme",
  "files": [
    "lib/**/*"
  ]
}

I tried a bunch of things including changing the references to use .js, using absolute paths instead, and changing some settings in tsconfig.json.

Why is Node.js not finding the submodules or would it be better to export the modules in a different way?

After compiling the ts files into js files, wherever you have import syntax, Node.js looks for .js files to resolve them. So it needs to be explicitly given a module name with .js extension in import.

You may need to read this doc on how the import mechanism works in Node.js.

To fix this issue, you have multiple choices(since the target you've defined is ES6):

1. change moduleResolution to nodeNext and add .js extension whenever you would importing modules in typescript:

import { EventBus } from "./modules/eventbus/eventbus.js";
import { EventHandler } from "./modules/eventbus/eventhandler.js";
import { EventType } from "./modules/eventbus/eventtype.js";
...

You don't need to be worried about it, typescript is well smart. Based on this comment from one of typescript contributor:

> .js file extensions are now allowed

2. Using rollup package. The rollup package won't manipulate your files. Instead, it bundles your output files.

Save time with npm link command

> I created a separate project to download this package from npm for an independent test.

First, you can use the handy npm link command to save yourself the trouble of uploading your package just so you can test. As per the docs the npm link command:

> ...is handy for installing your own stuff, so that you can work on it and test iteratively without having to continually rebuild.

Install your package as a dependency

With that out of the way, I think the hint is in the error message. Note it says:

> Cannot find module /workspaces/epic-engine-testing/node_modules/...

Here it seems Node is looking for the file in the epic-engine-testing project, so you must have the package.json file for the test project reference your package (i.e. the one you want to test). So go into your epic-engine-testing project folder and at the terminal type npm install epic-engine@0.1.0-dev.5. That should install your package so it can be found. If that doesn't resolve it, you'll need to share the package.json file for the epic-engine-testing to help us see what's going on.

Using the export { ... } from '...' syntax

Your main file can use the re-exports synax and be simplified to this when exporting:

export { EventBus } from "./modules/eventbus/eventbus";
export { EventHandler } from "./modules/eventbus/eventhandler";
export { EventType } from "./modules/eventbus/eventtype";
export { Event } from "./modules/eventbus/event";
export { SemVer } from "./modules/semver";

// the line below is not necessary when using above syntax.
// export { SemVer, Event, EventBus, EventHandler, EventType };