Error: Must use import to load ES Module - Using Typescript and Node

Question

Background

Tried to improve my error coding visibility and structure and decided to add the dependency ''' chalk ''', which requires Pure ESM. Originally, my ts.config/package.json was a common.js file and did not declare the "type" as "module". Made some changes as following chalk documentation and similar stack overflow troubleshooting. Upon reloading my app, I receive this error:

Error

[user] 
[user] > user@1.0.0 start
[user] > ts-node-dev src/index.ts
[user]
[user] [INFO] 02:43:13 ts-node-dev ver. 2.0.0 (using ts-node ver. 10.8.0, typescript ver. 4.7.2)
[user] Compilation error in /app/src/index.ts
[user] Error: Must use import to load ES Module: /app/src/index.ts
[user]     at Object.<anonymous> (/app/src/index.ts:1:7)
[user]     at Module._compile (node:internal/modules/cjs/loader:1105:14)
[user]     at Module._compile (/app/node_modules/source-map-support/source-map-support.js:568:25)
[user]     at Module.m._compile (/tmp/ts-node-dev-hook-07536074778072654.js:69:33)
[user]     at Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
[user]     at require.extensions..jsx.require.extensions..js (/tmp/ts-node-dev-hook-07536074778072654.js:114:20)
[user]     at require.extensions.<computed> (/tmp/ts-node-dev-hook-07536074778072654.js:71:20)
[user]     at Object.nodeDevHook [as .ts] (/app/node_modules/ts-node-dev/lib/hook.js:63:13)
[user]     at Module.load (node:internal/modules/cjs/loader:981:32)
[user]     at Function.Module._load (node:internal/modules/cjs/loader:827:12)
[user] [ERROR] 02:43:13 Error: Must use import to load ES Module: /app/src/index.ts

The following the changes I made to require requirements that I believe were neccessary?:

package.json

{
  "name": "user",
  "version": "1.0.0",
  "description": "",
  "type": "module",
  "main": "index.ts",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "ts-node-dev src/index.ts"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@types/bcrypt": "^5.0.0",
    "@types/cookie-parser": "^1.4.3",
    "@types/express": "^4.17.13",
    "@types/jsonwebtoken": "^8.5.8",
    "@types/morgan": "^1.9.3",
    "@types/multer": "^1.4.7",
    "axios": "^0.27.2",
    "bcrypt": "^5.0.1",
    "body-parser": "^1.20.0",
    "chalk": "^5.0.1",
    "cookie-parser": "^1.4.6",
    "cors": "^2.8.5",
    "dependencies": "^0.0.1",
    "dotenv": "^16.0.1",
    "express": "^4.18.1",
    "joi": "^17.6.0",
    "jsonwebtoken": "^8.5.1",
    "mongodb": "^4.6.0",
    "mongoose": "^6.3.3",
    "morgan": "^1.10.0",
    "multer": "^1.4.4",
    "nodemailer": "^6.7.5",
    "typescript": "^4.7.2",
    "uuid": "^8.3.2",
    "validator": "^13.7.0"
  },
  "devDependencies": {
    "nodemon": "^2.0.16",
    "ts-node-dev": "^2.0.0"
  }
}

index.ts

import mongoose from "mongoose";
import  app  from "./app";

const dbURI ='blabla' */
let PORT = 3000; /* process.env.PORT */

async function start() {

//T:              Connecting to MongoDB Database
    try{
        await mongoose
            .connect(dbURI)
            console.log(`connected to DB!`);        
    }catch(err) {
        console.log(err);
    };
    app.listen(PORT,()=>{
    console.log(
        `connected to PORT: ${PORT} and listening...although it may not bee that port`)
    });
}

start()

ts.config

{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    /* Basic Options */
    // "incremental": true,                   /* Enable incremental compilation */
    "target": "ESNext",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
    "module": "ESNext",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
     "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "composite": true,                     /* Enable project compilation */
    // "tsBuildInfoFile": "./",               /* Specify file to store incremental compilation information */
    // "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    "strict": true,                           /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,              /* Enable strict null checks. */
    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
    // "noUncheckedIndexedAccess": true,      /* Include 'undefined' in index signature results */

    /* Module Resolution Options */
    "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
   "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
    // "allowUmdGlobalAccess": true,          /* Allow accessing UMD globals from modules. */

    /* Source Map Options */
    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */

    /* Advanced Options */
    "skipLibCheck": true,                     /* Skip type checking of declaration files. */
    "forceConsistentCasingInFileNames": true  /* Disallow inconsistently-cased references to the same file. */
  },
  "include": [
    "src/**/*"
  ]
}

Edit:File I called chalk in to test

import express from "express";
import { NotFoundError } from "./errors/NotFoundError";
import errorHandler from "./middleware/error-handler";
import userIndex from "./routes/userIndex";
import morgan from "morgan"
import cookieParser from "cookie-parser";
import chalk from 'chalk'



const app = express();
app.use(express.json());
app.use(cookieParser());
app.set("trust proxy", true);

const log = console.log;


// I tried all methods below...
app.use(
    morgan(
    // "dev", 
    function (tokens, req, res) {
        return [
            chalk.red (tokens.method(req, res)),
            chalk.green(tokens.url(req, res)),
            chalk.yellow(tokens.status(req, res),"-"),
            chalk.bgBlueBright(tokens["response-time"](req, res), "ms"),
            chalk.cyan(tokens['date'](req, res),'web'),
            chalk.blue(tokens.res(req, res, "content-length")),
        ].join(" ");
    }) 
    ) 
    
log(chalk.red('I'm red'))
log(chalk.green(
    'I am a green line ' +
    chalk.blue.underline.bold('with a blue substring') +
    ' that becomes green again!'
));
log(chalk.rgb(123, 45, 67).underline('Underlined reddish color'));

    app.use(morgan( function (tokens, req, res) {
        return chalk.yellow(tokens['date'](req, res),'web')
        + ' ' + chalk.blue(tokens['remote-addr'](req, res))
        + ' ' + chalk.cyanBright(tokens.method(req, res))
        + ' ' + chalk.green(tokens.url(req, res))
        + ' ' + chalk.magentaBright(tokens.status(req, res))
        + ' ' + chalk.red(tokens['response-time'](req, res))
    }))


 app.use(morgan(`
:remote-addr :remote-user :method :url :status :res[content-length] - :response-time ms :date[web]
`)); 

app.use('/users', userIndex);

app.all("*", async (req, res, next) => {
    next(new NotFoundError());
});

app.use(errorHandler);

export default app ;

Answer 1

Seems that I have found a resolution after spending hours on that... I think it may help someone, as I've seen no such answer on Stackoverflow.

The problem was in ts-node-dev . No one would guess. But there is an open bug on that in their repo. Of course it has nothing to do with chalk . And of course as the first step one needs to fix the project to work with ESM as described in many places (a good explanation sits in chalk repo ).

To check it is ts-node-dev problem you may simply run tsc (original TS compiler) from your project root. It didn't output this 'import' error for me, and after I fixed a few other errors it compiled everything successfully.

Solution

So I uninstalled ts-node-dev and installed ts-node and nodemon instead, as recommended here .

First of all you may check the ts-node compilation and run attempt succeeds via:

node --loader ts-node/esm --inspect ./src/server.ts

Next, nodemon and ts-node should be run together to replace ts-node-dev :

From command line: nodemon --exec node --loader ts-node/esm src/server.ts

Or add it to scripts section in package.json (to use through npm run dev ):

"scripts": {
    ...
    "dev": "nodemon --exec node --loader ts-node/esm src/server.ts",
    ...
  },