Hard excercise from book "Programming Typescript", solved with a hack (type assertion). The objective is to prevent users from calling `.send` on a request that is missing `method` or `url` properties..

Request.ts

type Data =  {
  [key: string]: string | number | Data
}

type Method = 'GET' | 'POST' | 'PUT' | 'DELETE';

class Request {
  constructor(
    public url?: string,
    public data?: Data,
    public method?: Method,
  ) {}

  setMethod(method: Method): this & { method: Method } {
    this.method = method;

    // HACK ALERT, HACK ALERT
    return (<this & { method: Method}>this);
  }

  setUrl(url: string): this & { url: string } {
    this.url = url;

    // HACK ALERT, HACK ALERT
    return (<this & { url: string}>this);
  }

  setData(data: Data): this {
    this.data = data;
    return this;
  }

  send(this: this & { method: Method, url: string }): this {
    const { method, url, data } = this;

    console.log('Sending request', {
      method: method!,
      url: url!,
      data: data!
    });

    return this;
  }
}

// Funca, si no seteas el method y la url, TS va a chillar
new Request()
  .setMethod('GET')
  .setUrl('https://example.com')
  .setData({ asdf: 2 })
  .send()

export default Request