jQuery Post blob object gives Uncaught TypeError: Illegal invocation

I am trying to post a file using jQuery post, and get TypeError: Illegal invocation

function fbUpload(token){
  var dataURL = canvas.toDataURL('image/jpeg', 1.0)
  var blob = dataURItoBlob(dataURL)

  $.post( "https://graph.facebook.com/me/photos", {
    'access_token': token,
    'source': blob
  }, function( data ) {
    console.log(data);
  });
}

Could it be because of the 'blob'?

This is working fine:

function fbUpload(token){
  var dataURL = canvas.toDataURL('image/jpeg', 1.0)
  var blob = dataURItoBlob(dataURL)
  var formData = new FormData()
  formData.append('access_token', token)
  formData.append('source', blob)

  var xhr = new XMLHttpRequest();
  xhr.open( 'POST', 'https://graph.facebook.com/me/photos', true )
  xhr.onload = xhr.onerror = function() {
    console.log( xhr.responseText )
  };
  xhr.send( formData )
}