Handle file download from ajax post

Question

I have a javascript app that sends ajax POST requests to a certain URL. Response might be a JSON string or it might be a file (as an attachment). I can easily detect Content

Answer 1

I want to point out some difficulties that arise when using the technique in the accepted answer, i.e. using a form post:

1. You can't set headers on the request. If your authentication schema involves headers, a Json-Web-Token passed in the Authorization header, you'll have to find other way to send it, for example as a query parameter.

2. You can't really tell when the request has finished. Well, you can use a cookie that gets set on response, as done by jquery.fileDownload, but it's FAR from perfect. It won't work for concurrent requests and it will break if a response never arrives.

3. If the server responds with a error, the user will be redirected to the error page.

4. You can only use the content types supported by a form. Which means you can't use JSON.

I ended up using the method of saving the file on S3 and sending a pre-signed URL to get the file.