How to upload base64-encoded image from JavaScript?

I would like to upload a base64 encoded dataurl from browser(javascript) to a image file in Uploadcare please let me know, how do I do it (for that matter uploading any blob)?

You don't need to use base64 encoding, you can upload any blob object directly with uploadcare.fileFrom('object', file), where file is any JS file or blob object. If for whatever reason your image is encoded in base64, you will convert it to File or Blob object before passing to fileFrom function.