How to fix Cannot use module augmentation with import assignment in TypeScript

// ❌ Wrong - CommonJS import assignment
import express = require('express');
declare module 'express' {
  interface Request {
    user?: User;
  }
}

// ✅ Correct - ES6 import syntax
import * as express from 'express';
declare module 'express' {
  interface Request {
    user?: User;
  }
}

// ✅ Also correct - ES6 default import
import express from 'express';
declare module 'express' {
  interface Request {
    user?: User;
  }
}

{
  "compilerOptions": {
    "module": "ESNext",  // or "ES6", "ES2015", "ES2020", etc.
    // other options...
  }
}

{
  "compilerOptions": {
    "module": "CommonJS",     // Output format
    "moduleResolution": "node",
    "esModuleInterop": true,  // Important for compatibility
    "allowSyntheticDefaultImports": true
  }
}

// types/express.d.ts
import * as express from 'express';

declare module 'express' {
  interface Request {
    user?: User;
    timestamp?: number;
  }

  interface Response {
    jsonSuccess(data: any): void;
  }
}

{
  "compilerOptions": {
    // ...
  },
  "include": [
    "src/**/*",
    "types/**/*.d.ts"  // Include your declaration files
  ]
}

# Check if types are included
npm info @types/express  # For DefinitelyTyped packages
npm info express types   # For packages with built-in types

// types/express.d.ts
declare module 'express' {
  interface Request {
    user?: User;
  }
}
// No import needed - this is an ambient declaration

// test-augmentation.ts
import express from 'express';

const app = express();

// This should work if augmentation is correct
app.use((req, res, next) => {
  req.user = { id: 1, name: 'Test' };  // Augmented property
  req.timestamp = Date.now();          // Another augmented property
  next();
});

// Also test augmented methods
app.get('/', (req, res) => {
  res.jsonSuccess({ message: 'Hello' });  // Augmented method
});

npx tsc --noEmit test-augmentation.ts