“type”: “module” in package.json throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath)

I want to use import in my nodejs project instead of using require. So, I added,

"type": "module"

in my package.json.

import index from './index.js';

in server.js

when I run

node server.js

Error says,

internal/modules/cjs/loader.js:1174
      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: ....

server.conf.js is pasted below.

import express from 'express';

import http from 'http';
let app = express();
let server = http.createServer(app);

import morgan from 'morgan';
import methodOverride from 'method-override';;
import path from 'path';

let port = process.env.PORT || 4000;
app.use(morgan('dev'));
app.use(methodOverride('X-HTTP-Method-Override'));
let router = express.Router();
import routes from '../app/routes';
routes(app, router, client);
server.listen(port);
console.log(`Wizardry is afoot on port ${port}`);
export {
    app,
    client
};

Answer

According to stack-trace before you edit (https://stackoverflow.com/revisions/61558835/1):

internal/modules/cjs/loader.js:1174
      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: H:WORKSPACECMDsnode-basicserver.conf.js
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1174:13)
    at Module.load (internal/modules/cjs/loader.js:1002:32)
    at Function.Module._load (internal/modules/cjs/loader.js:901:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
    at internal/main/run_main_module.js:18:47 {
  code: 'ERR_REQUIRE_ESM'
}

I tried to locate the Node src who throws this error:

https://github.com/nodejs/node/blob/c24b74a7abec0848484671771d250cfd961f128e/lib/internal/modules/cjs/loader.js#L1234

// Native extension for .js
Module._extensions['.js'] = function(module, filename) {
  if (filename.endsWith('.js')) {
    const pkg = readPackageScope(filename);
    // Function require shouldn't be used in ES modules.
    if (pkg && pkg.data && pkg.data.type === 'module') {
      // ...
      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
    }
  }
  // ...
};

The comment Function require shouldn't be used in ES modules tells the js file to be loaded is an ES module, but the caller is trying to use require() function to load it.

Moreover, a double-check into Node src https://github.com/nodejs/node/blob/6cc94b2d7f69f1f541f7c5de3cb86e569fbd4aa3/lib/internal/errors.js#L1319 proves that H:WORKSPACECMDsnode-basicserver.conf.js is the ES module to be loaded.

So I’m trying to guess who is trying to load server.conf.js in your app but no luck. Most likely there is a require('./server.conf.js') in your index.js or somewhere else. If you find it just change it into import to fix.