Typescript cannot find module './lib'

Question

I am trying to use winston-aws-cloudwatch library in my server side app in Typescript.

I have a SSCCE setup on GitHub in case you want to reproduce the issue. Here is the detail.

index.ts

import logger  from './logger';
logger.info(`🚀🚀🚀 logger is up !!`);

logger.ts

import winston from 'winston';
import CloudWatchTransport from 'winston-aws-cloudwatch';

const logger = winston.createLogger();
logger.add(new CloudWatchTransport({logGroupName:'my-api', logStreamName: 'lstream'}));
logger.level = 'silly';

export default logger;

tsconfig.json

{
    "compilerOptions": {
    "target": "es2017" ,
    "module": "commonjs" ,
    "lib": [
        "es2017",
        "esnext.asynciterable"
    ] ,
    "allowJs": true ,
    "sourceMap": true ,
    "outDir": "./dist" ,    
    "noUnusedLocals": true ,
    "noUnusedParameters": true ,
    "noImplicitReturns": true ,
    "noFallthroughCasesInSwitch": true ,
    "moduleResolution": "node" ,
    "baseUrl": "./" ,
    "paths": {
        "*": ["node_modules/*", "src/types/*"]
    } ,
    "allowSyntheticDefaultImports": true ,
    "esModuleInterop": true 
    }
}

package.json

{
  "name": "winston-aws",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "ts-node index.js",
    "watch-node": "nodemon dist/index.js",
    "watch": "concurrently -k -p \"[{name}]\" -n \"TypeScript,Node\" -c \"yellow.bold,cyan.bold\" \"npm run watch-ts\" \"npm run watch-node\"",
    "watch-test": "npm run test -- --watchAll",
    "build-ts": "tsc",
    "watch-ts": "tsc --traceResolution -w"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "babel-cli": "^6.26.0",
    "winston": "^3.0.0",
    "winston-aws-cloudwatch": "^2.0.0"
  },
  "devDependencies": {
    "@types/node": "^10.3.3",
    "babel-preset-env": "^1.7.0",
    "concurrently": "^3.5.1",
    "nodemon": "^1.17.5",
    "ts-node": "^6.1.1",
    "typescript": "^2.9.2"
  }
}

When I try to run application using npm run watch I get:

[Node] internal/modules/cjs/loader.js:596
[Node]     throw err;
[Node]     ^
[Node]
[Node] Error: Cannot find module './lib/'
[Node]     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:594:15)
[Node]     at Function.Module._load (internal/modules/cjs/loader.js:520:25)
[Node]     at Module.require (internal/modules/cjs/loader.js:650:17)
[Node]     at require (internal/modules/cjs/helpers.js:20:18)
[Node]     at Object.<anonymous> (/Users/nishant/dev/sscce/dist/node_modules/winston-aws-cloudwatch/index.js:1:80)
[Node]     at Module._compile (internal/modules/cjs/loader.js:702:30)
[Node]     at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
[Node]     at Module.load (internal/modules/cjs/loader.js:612:32)
[Node]     at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
[Node]     at Function.Module._load (internal/modules/cjs/loader.js:543:3)

If you follow the execution, it seems Typescript was able to resolve the path:

[TypeScript] ======== Module name './lib/' was successfully resolved to '/Users/nishant/dev/sscce/node_modules/winston-aws-cloudwatch/lib/index.js'. ========

but I see node_modules/winston-aws-cloudwatch has a lib directory whereas dist/node_modules/winston-aws-cloudwatch does not.

At this point I am clueless what's going wrong.

Answer 1

Ah! So, after much trial and error it turned out the main culprit was:

 "allowJs": true ,

For some reason it was copying some parts of node_modules to ./dist one of those files was as you can see in the error:

dist/node_modules/winston-aws-cloudwatch/index.js

Now the problem was two fold

1. I did not know whether node_modules should be copied to dist. I thought all of it should go. Which is WRONG.

   None of node_modules should go in dist, the compiled files shall refer paths to figure out the location of node_modules.

2. The second problem was I could not see error go away when, in the fit of agony, I was switching on and off all the tsconfig options and rerunning the build. The reason was, dist DOES NOT CLEAR OFF. I figured this by an obscure luck while repeating the same process umpteenth time!

Anyway, good learning. Hope some of it would help someone someday.