client.js

function executeWithFetch(request) {
  // EXERCISE FOR THE READER
}

function executeWithAxios(request) {
  // EXERCISE FOR THE READER
}

function ClientBuilder() {
  return {
    forBaseUrl(baseUrl) {
      this.baseUrl = baseUrl;
      return this;
    },
    withHeaders(headers) {
      this.headers = headers;
      return this;
    },
    usingFetch() {
      this.executor = executeWithFetch;
      return this;
    },
    usingAxios() {
      this.executor = executeWithAxios;
      return this;
    },
    build() {
      return new Client(this.baseUrl, this.headers, this.executor);
    },
  }
}

class Client {
  constructor(baseUrl, headers, executor) {
    this.baseUrl = baseUrl;
    this.headers = headers;
    this.executor = executor;
  }

  post(endpoint, data) {
    const url = `${this.baseUrl}${endpoint}`;
    return this.executor({
      url,
      data,
      method: 'POST',
      headers: this.headers
    });
  }

  get(endpoint, params) {
    const url = `${this.baseUrl}${endpoint}`;
    return this.executor({
      url,
      params,
      method: 'GET',
      headers: this.headers
    });
  }
}