How does file upload work?

Question

JavaScript

Interested in how the download of files from the client (browser) to the server works. The mechanism itself is of interest in order to understand the implementation of that, that is already ready. Is ajax actually not downloading files asynchronously but doing something else.

Those. I select a file on the file system in the form. I click send. What is happening at that moment?

Answer 1

https://ru.wikipedia.org/wiki/Multipart/form-data
To better understand the mechanism, just look at the request body through the earnings panel in chrome or the firebug in ff when sending a post request with a file.