I have a png thumbnail with base64 data. I am trying to convert it to jpeg thumbnail. I am not sure what am I doing wrong. My current item has a blank thumbnail

var canvas = document.createElement('canvas');
canvas.id = currItem.Id + '_1';
canvas.width = currItem.ThumbnailInfo[0].Width;
canvas.height = currItem.ThumbnailInfo[0].Height;
var ctx = canvas.getContext('2d');

var p = new Promise((resolve, reject) => {

  var img = new Image();
  img.src = currItem.ThumbnailInfo[0].Thumbnail;
  img.onload = async function () {
    await ctx!.drawImage(img, 0, 0, canvas.width, canvas.height);
    var imageData = ctx?.getImageData(0, 0, canvas.width, canvas.height);
    ctx?.fillRect(0, 0, canvas.width, canvas.height);
    //var imageData = canvas.toDataURL();
    var imagejpeg = canvas.toDataURL('image/jpeg');
    resolve(imagejpeg);
  }
});

let imagejpgeg2 = await p;
currItem.ThumbnailInfo[0].Thumbnail = imagejpeg;