NestJS example

base-api.ts

/**
 * @file [Abstract Class] Base class for APIs to unify entrypoint for all implementations 
 * @version v1.0.0
 * @author LouisSung
 * @license MIT
 */

export abstract class BaseApi {
  protected readonly reqBody: {[key: string]: Json;};
  protected constructor(reqBody: {[key: string]: Json;}) {
    this.reqBody = reqBody;
  }
  public abstract entry(): Json;
}


// ===== Type Definitions =====
export type Json = null | boolean | number | string | Array<Json> | {[key: string]: Json;};

copycat.controller.ts

/**
 * @file [API Endpoint] Copycat endpoint (`/copycat`)
 * @version v1.1.0
 * @author LouisSung
 * @license MIT
 */

import {Body, Controller, Get, Post, Req} from '@nestjs/common';
import {Request} from 'express';

import {BaseApi, Json} from '../../core/base-api';


@Controller('copycat')
export class CopycatController {
  @Get(['/', '/get'])
  public copyGet(@Req()req: Request): ReqQuery & Hi {
    const hi: Hi = {host: req.hostname, method: req.method, mew: 'ฅ• ω •ฅ'};

    return {...(req.query as ReqQuery), ...hi};
  }

  @Post(['/', '/post'])
  public copyPost(@Req()req: Request, @Body()copycatDto: CopycatDto): SayHi {
    const hi: Hi = {host: req.hostname, method: req.method, mew: 'ฅ´• ω •`ฅ'};

    return {...copycatDto, ...hi};
  }

  @Post('/valid')
  public copyValid(@Req()req: Request, @Body()copycatDto: CopycatDto): SayHi {
    // @LS: Copycat is defined as class below
    // eslint-disable-next-line @typescript-eslint/no-use-before-define
    return new Copycat(req, copycatDto).entry();
  }
}

class Copycat extends BaseApi {
  protected readonly reqBody: CopycatDto & Hi;
  constructor(req: Request, copycatDto: CopycatDto) {
    const hi: Hi = {host: req.hostname, method: req.method, mew: 'ฅ´• ω •`ฅ'};

    super({...copycatDto, ...hi});
  }
  public entry(): SayHi { return {...this.reqBody, mew: 'ฅ`• ω •´ฅ'}; }
}


// ===== Type Definitions =====
interface ReqQuery {[key: string]: string | Array<string>;}
interface Hi {host: string; method: string; mew: 'ฅ• ω •ฅ' | 'ฅ´• ω •`ฅ' | 'ฅ`• ω •´ฅ';}

interface CopycatDto {[key: string]: Json;}
interface SayHi extends Hi, CopycatDto {}