<script type="text/javascript">

    function getBase64Image(img) {

      var canvas = document.createElement("canvas");

      canvas.width = img.width;

      canvas.height = img.height;

      var ctx = canvas.getContext("2d");

      ctx.drawImage(img, , , img.width, img.height);

      var dataURL = canvas.toDataURL("image/png");

      return dataURL

      // return dataURL.replace("data:image/png;base64,", "");

    }

    function main() {

      var img = document.createElement('img');

      img.src = './images/yeoman.png';

      img.onload =function() {

        var data = getBase64Image(img);

        console.log(data);

      }

      document.body.appendChild(img);

    }

    main()

  </script>