How do I force download with HTML/JavaScript?

Question

I have a link and, if a user clicks it, I need 2 things to happen:

• A proper HTTP response is sent to the user (especially with Content-Type: video/mp4

Answer 1

No, this is not possible (at least for values of JavaScript limited to client-side JavaScript).

If you want to override the default behavior of how a browser handles an HTTP resource, you need to do it with HTTP headers. If you want to do it correctly, use the content-disposition header (with an attachment value).

You can set this header using server-side JavaScript or (pretty much) any other server side environment.