I am currently uploading images pasted from the clipboard with the following code:
// Turns out getAsFile will return a blob, not a file
var blob = event.cli
Adding this here as it doesn't seem to be here.
Aside from the excellent solution of form.append("blob",blob, filename);
you can also turn the blob into a File
instance:
var blob = new Blob([JSON.stringify([0,1,2])], {type : 'application/json'});
var fileOfBlob = new File([blob], 'aFileName.json');
form.append("upload", fileOfBlob);