xhrRequest.js

  const encs = {json: 'application/json', text: 'text/plain', url: 'application/x-www-form-urlencoded', form: 'multipart/form-data'},
      xhrRequestDefaults = {method: 'POST', encoding: 'url', beforeCallback: function () {}, openedCallback: function () {}};
  /**
   * Make http request to url with object data as body
   * @param {string} url
   * @param {(object | string)} [data] - post data, formatting controlled by encoding
   * @param {object} [options] - object of options
   * @param {string} [options.encoding] - body encoding 'none', 'url', 'form', 'json', 'text' or mime (content) type, default: 'url'
   * @param {string} [options.contentType] - override automatic contentType, null disable automatic without sending one
   * @param {function} [options.method] - 'GET', 'POST', 'PUT', etc, default: 'POST'
   * @param {function} [options.beforeCallback] - callback before open(), params passed are (xhr, options)
   * @param {function} [options.openedCallback] - callback just after open(), params passed are (xhr, options)
   * @returns {Promise.<{ProgressEvent} event>}
   */
  module.xhrRequest = function (url, data, options) {
    const opts = Object.assign({}, xhrRequestDefaults, options || {}),
        xhr = new XMLHttpRequest(),
        enc = encs[opts.encoding] && opts.encoding || false, // false: custom content type
        body = data === undefined || enc === 'no-body' ? null : enc === 'form' ? new FormData() :
            enc === 'url' ? new URLSearchParams(data).toString() :
            typeof data === 'object' ? JSON.stringify(data) : data,
        contType = body === null ? null : enc && encs[enc] || opts.encoding;
    if (enc === 'form') {
      for (const key of Object.keys(data)) {
        body.append(key, data[key]);
      }
    }
    return new RSVP.Promise(function (resolve, reject) {
      xhr.addEventListener('load', function () { this.options = opts; resolve(this); });
      xhr.addEventListener('error', function () { this.options = opts; reject(this); });
      for (const event of Object.keys(opts.events || {})) {
        xhr.addEventListener(event, opts.events[event]);
      }
      opts.beforeCallback(xhr, opts);
      xhr.open(opts.method, url);
      opts.openedCallback(xhr, opts);
      if (opts.contentType !== null && (opts.contentType || contType)) {
        xhr.setRequestHeader('Content-Type', opts.contentType || contType);
      }
      for (const headerPair of opts.headers || []) {
        xhr.setRequestHeader(headerPair[0], headerPair[1]);
      }
      xhr.send(body);
    });
  };