如何扩展IncomingMessage类型的Request并完整克隆请求对象

尝试为Request添加body属性，编写了以下代码，但运行时提示新对象extRequest缺失request的19个方法，请问如何完整克隆request对象？

import { IncomingMessage, ServerResponse } from "http";

interface IRequest extends IncomingMessage {
  body: string;
}
export default (request: IncomingMessage, response: ServerResponse, next: (req: IncomingMessage, res: ServerResponse) => void) => {
    let data: Uint8Array[] = []
    request.on("data", dataChunk => {
        data.push(dataChunk)
    })
    request.on("end", () => {
        const body = Buffer.concat(data).toString();
        if (request.headers["content-type"] === "application/json"){
          const extRequest: IRequest = {...request};
          extRequest.body = body;
          next(extRequest, response)
        }
    })
    request.on("error", () => {
      response.statusCode = 500;
      response.write(`body isn't correct`);
      response.end();
    })
}

IncomingMessage是Node.js提供的类实例，它的方法都定义在原型链上。使用扩展运算符{...request}只能复制对象自身的可枚举属性，原型链上的方法不会被拷贝，所以新创建的extRequest会缺失这些方法。

方案1：直接类型断言（推荐） #

不需要克隆对象，直接对原request进行类型断言，添加body属性即可。JavaScript中对象是动态的，TypeScript只需类型断言就能绕过类型检查：

import { IncomingMessage, ServerResponse } from "http";

interface IRequest extends IncomingMessage {
  body: string;
}
export default (request: IncomingMessage, response: ServerResponse, next: (req: IncomingMessage, res: ServerResponse) => void) => {
    let data: Uint8Array[] = []
    request.on("data", dataChunk => {
        data.push(dataChunk)
    })
    request.on("end", () => {
        const body = Buffer.concat(data).toString();
        if (request.headers["content-type"] === "application/json"){
          // 类型断言为自定义的IRequest
          const extRequest = request as IRequest;
          extRequest.body = body;
          next(extRequest, response)
        }
    })
    request.on("error", () => {
      response.statusCode = 500;
      response.write(`body isn't correct`);
      response.end();
    })
}

方案2：完整克隆实例（不推荐） #

如果确实需要创建新实例，可通过Object.create继承原对象的原型，再用Object.assign复制自身属性：

// 在end事件回调中替换克隆逻辑
const extRequest = Object.create(Object.getPrototypeOf(request)) as IRequest;
Object.assign(extRequest, request);
extRequest.body = body;
next(extRequest, response);

注意：克隆IncomingMessage实例可能会导致原对象的事件监听、流状态等出现异常，除非有特殊需求，否则优先使用方案1。

内容的提问来源于stack exchange，提问作者Oksana