# Pastebin hma74J7W
var reader = new FileReader();

        reader.onload = function(e) {
          var fetchPromise = fetch(this.urlBase + url, {
            method: 'POST',
            mode: 'cors',
            redirect: 'follow',
            body: e.currentTarget.result
          });

          fetchPromise.then(function (response) {
            return response.json()
          }).then((function (json) {
            document.body.dispatchEvent(new CustomEvent(eventKey, {detail: json}));
          }).bind(this))
        }.bind(this);

        reader.readAsText(new Blob([body.arg]));