Adjustments for TypeScript

1. Setup
2. Working with Middleware
3. Working with Mongoose Model Methods

Setup

Do the following as part of the setup for a TypeScript app:

• Generate tsconfig using npx tsc --init
• Enable tsconfig’s outDir setting and set it to ./dist - this compiles your TypeScript code in that folder and runs index.js from there
• Change the scripts in package.json:
  • "build": "npx tsc"
  • "start": "node dist/index.js"
  • "dev": "concurrently \"npx tsc --watch\" \"nodemon -q dist/index.js\""
• Compile the app for the first time with npm run build
• You can now launch the dev server with npm run dev without any errors

Working with Middleware

Middleware functions typically pass info down to the next middleware functions by adding properties to the request object. However, you can only do this in TypeScript by extending the Request type.

The way to do this in TypeScript is to extend the Request type:

1. In src, create a types folder with an express folder in it.
2. Create a file index.d.ts in the folder types/express.

3. Add your required properties in the index.d.ts file:

    declare namespace Express {
      interface Request {
        yourNewProperty?: string;
      }
    }
   

4. Add the ./types (or ./src/types) folder into the typeRoots option in tsconfig.json.

Working with Mongoose Model Methods

It is possible to define custom methods on Mongoose models in vanilla JavaScript. However, once again, you can only do this in TypeScript by creating interfaces for your model methods.

Process:

1. Create an interface for the model’s methods.

    interface IUserMethods {
      getName(): string;
      createJWT(): string;
      checkPassword(candidatePassword: string): boolean;
    }
   

2. Create a model type that recognises both (1) the interface for the schema and (2) the interface for the method(s):

    type IUserModel = Model<IUserSchema, {}, IUserMethods>;
   

3. When defining the actual Mongoose model, specify the schema and type:

    const User = model<IUserSchema, IUserModel>('User', UserSchema)
   

For more examples, refer to the Mongoose documentation on TypeScript.