Issue of addText() in  /src/SketchField.jsx 
Inside the function, the code should be 
***
 Object.assign(opts, options);
    iText.set({
      'left': opts.left,
      'top': opts.top
    });
***
instead of

***
 Object.assign(options, opts);
    iText.set({
      'left': options.left,
      'top': options.top
    });
***