decorator.ts

export const Param = (name) => (target: any, propertyKey: string, index: number)  => {
    // Set parameter name.
    Reflect.defineMetadata('param', name, target, propertyKey);
}

export const Get = (url) => (target: any, propertyKey: string)  => {
    // Set method and url.
    Reflect.defineMetadata('route', { method: 'get', url }, target, propertyKey);
}

controller.ts

import { Get, Param } from 'decorator.ts';

class Controller {
    @Get('/:id')
    async findUser (
        @Param('id') id: string | undefined 
      ): Promise<User> {
    }
}

server.ts

import { Controller } './controller.ts'

const router = require('express').Router();

for (let propertyKey of Object.getOwnPropertyNames(Controller.prototype)) {
   // Read metadata created by decorators.
   var param = Reflect.getMetadata('param', target, propertyKey);
   var route = Reflect.getMetadata('method', target, propertyKey);

   // Add routes using data from decorators.
   router[route.method]('route.url', (req, res) => {
   // Call needed method of controller.
       return Controller[propertyKey](req.params[param]);
   });
}