_updateHandleAndProgress(newValue) {
      const max = this._effectiveMax;
      const min = this._effectiveMin;
      // The progress (completed) percentage of the slider.
      this._progressPercentage = (newValue - min) / (max - min);
      // How many pixels from the left end of the slider will be the placed the affected  by the user action handle
      this._handlePositionFromStart = this._progressPercentage * 100;
    }
Updates the UI representation of the progress bar and handle position

@private