Validation & Serialization

mion uses Deepkit's runtime types to automatically Validate request params and Serialize/Deserialize request/response data.

Thanks to Deepkit's magic the type information is available at runtime and the data can be "auto-magically" Validated and Serialized.

Deepkit is also a fully featured Typescript framework but has a completely different philosophy than mion. For more information please read Deepkit's documentation!

Please note we only use the @deepkit/type package from Deepkit

Explicit Types!

Type Inference is not supported so parameter types and specially return types must be explicitly defined.

๐Ÿšซ Incorrect route definitions:

const myNullRoute = () => null; 
const sayHello = (ctx, name) => `Hello ${name}`;
const getDummyUser = () => { 
    return new User({name: 'James', surname: 'Smith'})
const getUser = async (ctx, userId) => {
    return data.getUserById(userId);

โœ… Correct route definitions:

const myNullRoute = (): null => null;
const sayHello = (ctx: Context, name: string): string => `Hello ${name}`;
const getDummyUser = (): User => {
    return new User({name: 'James', surname: 'Smith'})
const getUser = async (ctx: Context, userId: number): Promise<User> => {
    return data.getUserById(userId);

Configuring ESLint

It might be a good idea to enforce explicit types in router files, but having to explicitly declare types everywhere can be a bit annoying.

We recommend using a suffix in your router files i.e: .routes.ts and configure ESLint to enforce explicit types only on those files.

/* file: .eslintrc.js */
module.exports = {
  root: true,
  parser: '@typescript-eslint/parser',
  plugins: ['@typescript-eslint'],
  extends: ['eslint:recommended', 'plugin:@typescript-eslint/recommended'],
  parserOptions: {
    project: [
        './packages/*/tsconfig.json' // use only in monorepos 
  // adds explicit types rules to .routes.ts files 
  overrides: [
      files: ['**/*.routes.ts'],
      rules: {
        '@typescript-eslint/explicit-function-return-type': 'error',
        '@typescript-eslint/no-explicit-any': 'error',