I build a expressJs app by ES6 and I got the below error:

```
(node:4132) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/run_main.js:54
    internalBinding('errors').triggerUncaughtException(
                              ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module 'E:\wamp64\www\myDemos\nodeJs\expressJsExample\config\app' imported from E:\wamp64\www\myDemos\nodeJs\expressJsExample\server.mjs
←[90m    at finalizeResolution (internal/modules/esm/resolve.js:255:11)←[39m
←[90m    at moduleResolve (internal/modules/esm/resolve.js:603:10)←[39m
←[90m    at Loader.defaultResolve [as _resolve] (internal/modules/esm/resolve.js:644:13)←[39m
←[90m    at Loader.resolve (internal/modules/esm/loader.js:94:40)←[39m
←[90m    at Loader.getModuleJob (internal/modules/esm/loader.js:240:28)←[39m
←[90m    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:42:40)←[39m
←[90m    at link (internal/modules/esm/module_job.js:41:36)←[39m {
  code: ←[32m'ERR_MODULE_NOT_FOUND'←[39m
}
[nodemon] app crashed - waiting for file changes before starting...

```

If I use `import app from './config/app.js';` then working but if I use `import app from './config/app';` then return the above error.

The below is my code:

**package.json**

```
{
  "name": "ExpressJsExample",
  "version": "1.0.0",
  "description": "Express Js Example",
  "main": "server.js",
  "type": "module",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "nodemon server.js"
  },
  "author": "Mukesh Singh Thakur",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.19.0",
    "chalk": "^4.0.0",
    "dotenv": "^8.2.0",
    "express": "^4.17.1",
    "http": "0.0.1-security",
    "http-errors": "^1.7.3",
    "jsonwebtoken": "^8.5.1",
    "nodemon": "^2.0.2",
    "pg": "^8.0.0",
    "request": "^2.88.2",
    "sequelize": "^5.21.6"
  },
  "devDependencies": {
    "sequelize-cli": "^5.5.1"
  }
}

```

**server.js**

```
import http from 'http';
import app from './config/app';

const server = http.Server(app);
server.listen(3000, () => {
       return true;
});

```

**app.js**

```
import express from 'express';
const app = express();

export default app;

```

The example app is available in `https://github.com/msthakur08/express-js-example` URL. The example files import with '.js' existence but I want to import file without '.js' existence.