index.js

export default class RestClient {
  constructor (baseUrl = '', { headers = {}, devMode = false, simulatedDelay = 0 } = {}) {
    if (!baseUrl) throw new Error('missing baseUrl');
    this.headers = {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    };
    Object.assign(this.headers, headers);
    this.baseUrl = baseUrl;
    this.simulatedDelay = simulatedDelay;
    this.devMode = devMode;
  }

  _simulateDelay () {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve();
      }, this.simulatedDelay);
    });
  }

  _fullRoute (url) {
    return `${this.baseUrl}${url}`;
  }

  _fetch (route, method, body, isQuery = false) {
    if (!route) throw new Error('Route is undefined');
    var fullRoute = this._fullRoute(route);
    if (isQuery && body) {
      var qs = require('qs');
      const query = qs.stringify(body);
      fullRoute = `${fullRoute}?${query}`;
      body = undefined;
    }
    let opts = {
      method,
      headers: this.headers
    };
    if (body) {
      Object.assign(opts, { body: JSON.stringify(body) });
    }
    const fetchPromise = () => fetch(fullRoute, opts);
    const extractResponse = response =>
      response.text().then(text => text? JSON.parse(text) : undefined);

    if (this.devMode && this.simulatedDelay > 0) {
      // Simulate an n-second delay in every request
      return this._simulateDelay()
        .then(() => fetchPromise())
        .then(extractResponse);
    } else {
      return fetchPromise()
        .then(extractResponse);
    }
  }

  GET (route, query) { return this._fetch(route, 'GET', query, true); }
  POST (route, body) { return this._fetch(route, 'POST', body); }
  PUT (route, body) { return this._fetch(route, 'PUT', body); }
  DELETE (route, query) { return this._fetch(route, 'DELETE', query, true); }
}