This module is declared with using 'export =', and can only be used with a default import when using the 'esModuleInterop' flag

Question

I'm trying to make a simple API using typescript and NodeJS but when I run my code I get this error

"This module is declared with using 'export =', and can only be used with a default import when using the 'esModuleInterop' flag."

This is my code: package.json

    {
  "name": "API-Proyecto",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.17.1",
    "jsonwebtoken": "^8.5.1"
  },
  "devDependencies": {
    "@types/cors": "^2.8.6",
    "@types/express": "^4.17.6",
    "nodemon": "^2.0.4"
  }
}

Index.ts

    import express from 'express';
import { Request, Response }  from 'express';
import cors from 'cors';

const app = express();

app.use(express.urlencoded({extended: true}));
app.use(express.json);
app.use(cors({origin: true, credentials: true}));

app.get('/api/auth/testing', (req: Request, res: Response) =>{
    res.status(200).json({
        ok : true,
        msg : 'hi from my method'
    });
});

app.listen(3000, () => {console.log('Server running on 3000' )});

tsconfig.json

    {
  "compilerOptions": {
    "target": "es6",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    "outDir": "./dist",                        /* Redirect output structure to the directory. */
    "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
  }
}

Answer 1

Your code is perfectly fine.

Fix

When you make changes to tsconfig, sometimes you need to restart your IDE or Code Editor 🌹

Answer 2

Use:

import * as express from 'express';

Answer 3

My problem was that I tried to run tsc as tsc -w index.ts.

However, as said here https://stackoverflow.com/a/33244030/5711655 if you run tsc with a specified input file, it won't use the tsconfig.json in your project directory! So in my case I had to use tsc -w.

Answer 4

I fixed similar mistake for yourself. I use project (vite + vue 3 + ts)

1. added on tsconfig.json->compilerOptions + "moduleResolution": "node".
2. import moment from "moment" to import * as moment from "moment";

UPD:- and add this setting,

"allowSyntheticDefaultImports": true

and then I can use, import moment from "moment";

Answer 5

I was able to solve it by setting the "esModuleInterop" property to true inside the "compilerOptions" object in the tsconfig.json file.

{
  "compilerOptions": {
    "esModuleInterop": true,
    ...
  },
}

Answer 6

Don't forget to set "moduleResolution": "node" in the tsconfig.json if you are using node.

Answer 7

When working with Typescript you you need to add a flag on your tsconfig.json file that allows synthetic Imports as so:

• open tsconfig.json
• add:

{
  "compilerOptions": {
    "jsx": "react",
    "module": "es6",
    "target": "es6",
    "moduleResolution": "node", 
    "allowSyntheticDefaultImports": true
  }
}

Answer 8

I solved the problem by compiling the whole file instead of compiling individual files.

Just run the following command to compile the whole file in a go

npx tsc

This should solve your problem

Answer 9

As with most answers here, I have tested a wide variety of settings in the tsconfig.json file and none have resolved my issue.

Response: In the end, I needed to change the way I am importing the express module:

server.ts:

import express = require('express'); //! import express from 'express';
import { Express, Request, Response } from 'express';

const SERVER_PORT: number = 3000;

const app: Express = express();

app.use(express.json());

app.get("/", (request: Request, response: Response) => {
    return response.json({ message: "Hello world!!!" });
});

app.listen(SERVER_PORT, () => {
    console.log(`Server running at: http://localhost:${SERVER_PORT}`);
});

And tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "types": ["node", "express"],
    "lib": [
            "ES2020",
            "DOM",
        ],
    "allowJs": true,
    "sourceMap": true,
    "outDir": "./dist",
    "rootDir": "./src",
    "strict": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "resolveJsonModule": true
  }
}

Answer 10

You should set:

esModuleInterop in your ts.config.json to TRUE.

{
  "compilerOptions": {
    "lib": ["es5", "es6"],
    "target": "es5",
    "module": "commonjs",
    "moduleResolution": "node",
    "outDir": "./build",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "sourceMap": true,
    "esModuleInterop": true
  }
}

Answer 11

FWIW, I found that switching from

import * as blah from 'blah-lib';

To

const blah = require('blah-lib');

Fixed the issue at compile time.

Answer 12

Just like @basarat said rightfully, restarting Typescript can fix this issue. I already included "esModuleInterop": true, in tsconfig.json. I want to add, that you can do this via the Intellij Footer as well. Click on your Typescript version there.

Thanks for the help.

Answer 13

I was wondering a lot but a friend helped me:

1. You need to create a command inside of "scripts" part on package.json

Package.json

{
  "name": "api-proyecto",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    **"build-dev": "tsc -w"**
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/cors": "^2.8.6",
    "@types/express": "^4.17.6"
  },
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.17.1"
  }
}

2. To run your script you need to type the following line

   npm i run build-dev (because it's the name of our command)

3. Finally in another powershell launch node normally. For Example:

   node .\dist\index.js

Answer 14

After trying all of the above solutions to no avail, I stumbled upon a solution for my case. I don't know why this works but running tsc instead of tsc index.ts or tsc --watch index.ts compiled fine. This error makes no sense to me at all. If someone can enlighten me and other readers of this post, it would be greatly appreciated.

Answer 15

I tried everything on this thread and it didn't work. What finally did was swapping tsc for ts-node to compile typescript in the app.

For reference I had this problem in a rushjs monorepo which may have further confused tsc

Answer 16

I had the same issue with my vscode, the error keeps on popping even with changing the tsconfig.json.

The problem was that tsconfig.json was extending from expo/tsconfig.base and somehow vscode didn't detect it.

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "src/*": ["src/*"],
      "static/*": ["static/*"]
    }
  },
  "extends": "expo/tsconfig.base"
}

I just opened this expo/tsconfig.base with right click and then save it to make vscode aware of this.

Answer 17

Try to write:

import express = require('express');

It should work.