code: function (format, quality) {
        var canvasEl = this.upperCanvasEl || this.lowerCanvasEl;
  
        this.renderAll(true);
        var data = (fabric.StaticCanvas.supports('toDataURLWithQuality'))
                     ? canvasEl.toDataURL('image/' + format, quality)
                     : canvasEl.toDataURL('image/' + format);
        this.renderAll();
        return data;
      }
docs: Exports canvas element to a dataurl image.
  @method toDataURL
  @param {String} format the format of the output image. Either "jpeg" or "png".
  @param {Number} quality quality level (0..1)
  @return {String}