code: function readFailureCallback(e) {
      if (this._readyState === FileReader.DONE) {
          return;
      }
  
      this._readyState = FileReader.DONE;
      this._result = null;
      this._error = new FileError(e);
  
      if (typeof this.onerror === "function") {
          this.onerror(new ProgressEvent("error", {target:this}));
      }
  
      if (typeof this.onloadend === "function") {
          this.onloadend(new ProgressEvent("loadend", {target:this}));
      }
  }
docs: Callback used by the following read* functions to handle errors.
  Must be bound to the FileReader's this, e.g. readFailureCallback.bind(this)