How to give a Blob uploaded as FormData a file name?

For Chrome, Safari and Firefox, just use this:

form.append("blob", blob, filename);

(see MDN documentation)

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);