Actually XHR stands for XMLHttpRequest (and https://en.wikipedia.org/wiki/XMLHttpRequest). So I *guess* whatever you send, e.g. JSON, is wrapped inside an XML envelope.

Also be advised that you do not need (depending on Browser+version) to have a Form created already in HTML in order to ajax images over. In your ajax'er function you can create the Form on the fly and add File objects (e.g. images) and JSON and all in a way similar to hash. But you definetely do not need to ASCII-fy your binary data as you can use a Blob . I do not know how they send that Blob. But, logically thinking, since they wrap it inside an XML envelope all will be ASCII-fied. Sorry for ... oh I am lost in all these zoological metaphors you used.

This may also be of help https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Sending_and_Receiving_Binary_Data

Just to drive my last post's point home: Create one js function to do all the ajax'ing you will ever need, with nested data structures (as JSON) and binary or other file uploads. Add all the error handling code there and of course, since it is all asynchronous you need to be prepared to supply function pointers to handling success and failure. On the server side, create a POST data "untangler" which will handle all that your ajax can send and return a complex (hash) data back with status code, data and html-or-text-or-both message. Make sure you test unicode support (e.g. for error messages or data-input or db-data-out-to-browser) through these two functions. I found Mojolicious helpful for the server-side. And as people say here, benchmark it before making any assumptions. And for the browser-side I prefered to build my AJAX function from pure-js in its own little library (js file) which now I use for all my needs. All I needed was online.

BTW, AJAX is an acronym for Asynchronous JavaScript And XML but Ajax was the legendary greek hero maddened by some immature bunch of Gods and committed suicide out of shame, famously depicted by Exekias in this fine art specimen . And let's not go into football but Omonoia famously beat Ajax 4-0 in 1979 with a Bulgarian coach (another legend: Arsov) and all-native footballers. (allow me, oh fellow Monks, the post-festive, over-locked-down delirium).

bw, bliako