This example shows the implementation of a method which uses a Promise to report the success or failure of an XMLHttpRequest.

Ajax + Promise

      function ajax(options) {
        "use strict";

        let promise = new Promise((resolve, reject) => {
          let xhr = new XMLHttpRequest();
          let method = options.method || "GET";
          let url = options.url || null;
          let data = options.data || null;
          let responseType = options.responseType || "text";

          function serialize(obj) {
            let argCount = 0;
            let str = "";

            for (let key in obj) {

              if (obj.hasOwnProperty(key)) {
                if (argCount++) {
                  str += "&";
                }
                str += `${encodeURIComponent(key)}=${encodeURIComponent(obj[key])}`;
              }
            }

            return str;
          }

          xhr.open(method, url);

          if (method === "POST" || method === "PUT") {
            if (data && typeof data === "object") {
              data = serialize(data);
              xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
            }
          }

          xhr.onload = function() {
            if (this.status >= 200 && this.status < 300) {
              resolve(this.response)
            } else {
              reject(this.statusText)
            }
          };

          xhr.responseType = responseType;
          xhr.send(data);
        });

        return promise;
      }

      var data = ajax({
        method: "POST",
        responseType: "json",
        url: "http://localhost:3000/api/comments",
        data: {
          "author": "Fábio Dan",
          "text": "Lorem ipsum"
        }
      }).then((response) => {
        console.log(response);
      }).catch((error) => {
        console.error(error);
      });