Convert URL to File or Blob for FileReader.readAsDataURL

To convert a URL to a Blob for FileReader.readAsDataURL() do this:

var request = new XMLHttpRequest();
request.open('GET', MY_URL, true);
request.responseType="blob";
request.onload = function() {
    var reader = new FileReader();
    reader.readAsDataURL(request.response);
    reader.onload =  function(e){
        console.log('DataURL:', e.target.result);
    };
};
request.send();