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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:
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 };
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:
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");
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?

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 };

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

Unable to run JEST test

I'm facing an issue when I try to import something using require() function in jest test file.
script2.test.js
const fetch = require('node-fetch');
it('test function', () => {
expect(4).toEqual(4);
});
Package.json
{
"name": "jest-test",
"version": "1.0.0",
"description": "",
"type": "module",
"scripts": {
"test": "jest --watchAll"
},
"keywords": [],
"author": "",
"license": "ISC",
"devDependencies": {
"#babel/cli": "^7.15.7",
"#babel/core": "^7.15.8",
"#babel/plugin-transform-async-to-generator": "^7.14.5",
"#babel/preset-env": "^7.15.8",
"jest": "^27.3.1"
},
"dependencies": {
"node-fetch": "^3.0.0"
},
"jest": {
"transform": {
"^.+\\.(js|jsx)$": "babel-jest"
}
}
}
babel.config.cjs
module.exports = {presets: ['#babel/preset-env']}
I'm getting following errors when I run the test using npm test
FAIL ./script2.test.js
● Test suite failed to run
Jest encountered an unexpected token
Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.
Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.
Details:
C:\work\jest-udemy\node_modules\node-fetch\src\index.js:9
import http from 'http';
^^^^^^
SyntaxError: Cannot use import statement outside a module
> 1 | const fetch = require('node-fetch');
| ^
I'm new to JEST, any help is much appreciated.
My Node version is 14.17.3
Thanks you.

It seems that one still needs to jump through the hoops to make jest work with ESM.
In package.json change your script to:
"test": "node --experimental-vm-modules node_modules/jest/bin/jest.js --watchAll"
And in script2.test.js use import:
import fetch from 'node-fetch';
P.S. This was tested with node 14.15.1

how can I use top level "await" in typescript next.js

When I use "await" on top-level like this:
const LuckyDrawInstance=await new web3.eth.Contract(abi)
I got a warning on the terminal: "set experiments.topLevelAwait true". When I tried to add this to "tsconfig.json", it still does not work. it says "experiments" property does not exist.
I could wrap it inside an async function but I want to set it without a wrapped function.

It is nothing to do with the tsconfig.json. You have to set it inside next.config.js. New version of next.js uses webpack5 and webpack5 supports top level await.
module.exports = {
webpack: (config) => {
// this will override the experiments
config.experiments = { ...config.experiments, topLevelAwait: true };
// this will just update topLevelAwait property of config.experiments
// config.experiments.topLevelAwait = true
return config;
},
};
NOTE
You have to use it outside the functional component:
export default function Navbar() {
// this will throw error
// Syntax error: Unexpected reserved word 'await'.
const provider=await customFunction()
return (
<section>
</section>
);
}
Warning
Since it is experimental, it might be broken in some versions

The latest solution as of writing this post that worked for me is using Babel instead of SWC since Next.js does not allow custom SWC configuration, therefore, you cannot allow topLevelAwait through .swcrc file.
Add Babel plugin called #babel/plugin-syntax-top-level-await into your package.json.
eg.
{
"devDependencies": {
"#babel/plugin-syntax-top-level-await": "^7.14.5"
}
}
Create .babelrc file in the root directory of your project where package.json lives.
Inside .babelrc make sure to include next/babel preset and the topLevelAwait plugin.
eg.
{
"presets": ["next/babel"],
"plugins": [
"#babel/plugin-syntax-top-level-await"
]
}
This is the easiest solution until Next.js team allows us to include SWC configuration. Note that by doing this you will not have SWC performance benefit since it will be disabled in favor of Babel.

I have been struggling with this for 2-3 days. Here is a solution that works. Please follow the following steps.
1. Copy paste the following in your package.json
{
"name": "projectname",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "mocha",
"dev": "next dev"
},
"author": "",
"license": "ISC",
"dependencies": {
"#truffle/hdwallet-provider": "^2.0.1",
"fs-extra": "^10.0.0",
"ganache-cli": "^6.12.2",
"mocha": "^9.1.4",
"next": "^12.0.8",
"react": "^17.0.2",
"react-dom": "^17.0.2",
"solc": "^0.8.9",
"web3": "^1.7.0",
"#babel/plugin-syntax-top-level-await": "^7.14.5"
},
"devDependencies": {
"#babel/plugin-syntax-top-level-await": "^7.14.5"
}
}
2. Delete your node_modules folder
3. Goto your project's root directory and reinstall all the packages using npm install command
4. Create a new file in your project's root directory and call it "next.config.js"
5. Copy paste following code in next.config.js file and save.
module.exports = {
// target: 'experimental-serverless-trace',
webpack: (config) => {
config.experiments = config.experiments || {};
config.experiments.topLevelAwait = true;
return config;
},
};

'ReferenceError: jest is not defined' when running unit test

I'm in the early stages of a new app that so far just uses vanilla JS. I'm trying to use ES6 modules for my Jest unit tests, so I followed the 2020 updated instructions on making this possible.
However, after following those instructions, I get the error ReferenceError: jest is not defined when running my unit test.
Here's my package.json:
{
"version": "1.0.0",
"main": "app.js",
"type": "module",
"jest": {
"testEnvironment": "jest-environment-node",
"transform": {}
},
"scripts": {
"test": "node --experimental-vm-modules node_modules/jest/bin/jest.js",
"start": "node server.js"
},
"license": "ISC",
"devDependencies": {
"express": "^4.17.1",
"jest": "^26.6.3",
"jest-environment-node": "^26.6.2",
"open": "^7.3.0"
},
"dependencies": {}
}
Below is my test file. The error occurs due to the jest.fn call:
import { getTotalNumPeople } from "./app.js";
test("Get total number of people", async () => {
global.fetch = jest.fn(() => Promise.resolve({
json: () => Promise.resolve({count: 15})
})
)
expect(await getTotalNumPeople()).toBe(15);
});
Any ideas on why this is happening? I'm confident that the issue has to do with the steps I followed to support ES6 modules. Prior to these changes, my test ran fine when I simply pasted the getTotalNumPeople function in my test file.
If I comment out mocking my function, I then get a ReferenceError about fetch not being defined (since getTotalNumPeople uses fetch). So it's not just jest that's not defined.
I notice that if I do not specify jest-environment-node as my test environment, the error changes to ReferenceError: global is not defined due to referring to global.fetch in my test. Just thought I'd note that in case that helps.

It looks like you didn’t import jest, so you have to just add this line to the top of the file:
import {jest} from '#jest/globals'
For more details, see this issue on native support for ES6 modules in Jest.

while essentially the same as the answer of Rupesh - you can expose jest globally without having to import it in each test file - by adding a setup-file to the jest configuration:
"jest": {
"setupFiles": [
"<rootDir>/test-setup.js"
]
}
then add this to test-setup.js:
import { jest } from '#jest/globals';
global.jest = jest;
also in general ESM support for jest is improved by a test script in package.json as so:
"scripts": {
"test": "node --no-warnings --experimental-vm-modules $( [ -f ./node_modules/.bin/jest ] && echo ./node_modules/.bin/jest || which jest )"
},

Jest testing with ES6 Modules (without babel) [duplicate]

Is it possible to test ES6 Modules with Jest without esm or babel? Since node v13 supports es6 natively have tried:
//package.json
{
…
"type": "module"
…
}
//__tests__/a.js
import Foo from '../src/Foo.js';
$ npx jest
Jest encountered an unexpected token
…
Details:
/home/node/xxx/__tests__/a.js:1
import Foo from '../src/Foo.js';
^^^^^^
SyntaxError: Cannot use import statement outside a module
When babel is added a transpiler, it works, but can es6 modules be used natively as well?

Yes, it is possible from jest#25.4.0. From this version, there is a native support of esm, so you will not have to transpile your code with babel anymore.
It is not documented yet, but according to this issue you have to do 3 easy steps to achieve that (At the time of writing this answer):
Make sure you don't transform away import statements by setting transform: {} in your jest config file
Run node#^12.16.0 || >=13.2.0 with --experimental-vm-modules flag
Run your test with jest-environment-node or jest-environment-jsdom-sixteen.
So your jest config file should contain at least this:
export default {
testEnvironment: 'jest-environment-node',
transform: {}
...
};
And to set --experimental-vm-modules flag, you will have to run Jest from package.json as follows (I hope this will change in the future):
"scripts": {
"test": "node --experimental-vm-modules node_modules/jest/bin/jest.js"
}
I hope, this answer was helpful to you.

Note that this is is still experimental, but we have documented how to test this, so there's hopefully less confusion.
https://jestjs.io/docs/en/ecmascript-modules
The steps in https://stackoverflow.com/a/61653104/1850276 are correct

I followed the tips provided in the accepted answer, but I added the property "type": "module" in my package.json in order to jest works properly. This is what I done:
In package.json:
"devDependencies": {
"jest": "^26.1.0",
"jest-environment-jsdom-sixteen": "^1.0.3",
"jest-environment-node": "^26.1.0"
},
"scripts": {
"test": "node --experimental-vm-modules node_modules/jest/bin/jest.js"
},
"type": "module",
"jest": {
"transform": {},
"testEnvironment": "jest-environment-jsdom-sixteen"
}

To run jest from "jest" extension in VSCode with "--experimental-vm-modules" flags, put this config in your global or workspaces settings.json:
"jest.nodeEnv": {
"NODE_OPTIONS": "--experimental-vm-modules"
}

In addition to #Radovan Kuka's answer, here's how to run Jest with ES modules, using npx:
"test:monitoring": "npx --node-arg=--experimental-vm-modules jest -f monitoring.test.js --detectOpenHandles",
The benefit is that one doesn't need to provide the absolute node_modules path.

Without Babel, here's a complete, minimal example that works on recent Jest versions. Run with npm test.
$ tree -I node_modules
.
├── package.json
├── src
│   └── foo.js
└── __tests__
└── foo.spec.js
package.json:
{
"type": "module",
"scripts": {
"test": "NODE_OPTIONS=--experimental-vm-modules jest"
},
"devDependencies": {
"jest": "^29.3.1"
}
}
src/foo.js:
export const bar = () => 42;
__tests__/foo.spec.js:
import {bar} from "../src/foo";
describe("foo.bar()", () => {
it("should return 42", () => {
expect(bar()).toBe(42);
});
});
The secret sauce is in the package.json: "type": "module" and NODE_OPTIONS=--experimental-vm-modules jest.
If you want to add a mock, it's a bit complicated. See this answer.