javascript - What problems may using the MIME type application/json cause?

Question

I am working on a web service the needs to return JSON data. I read that I should use application/json but am not sure what problems this may cause?

For example, will older browsers support it? (IE6+, FF, Opera, etc.)

Or is it possible that users behind corporate firewalls/proxy servers block the mime type application/json?

What, if any, problems have you had following this advice?

Answer 1

Let's consider IE. Say you have a hidden iFrame which you use to request a file download. For example

<iframe src="getFile?id=123">

Now, the server may send a JSON-encoded error message like

{
    error: 'File 123 does not exist',
    retryLater: false
}

If that error message is sent as application/json, a download dialog will appear, because the JSON text is mistaken for the actual file.

On the other hand, a MIME type of text/plain will cause the message to be rendered in the iFrame, and you can extract it, and transform it into a fancy pop-up or something using JScript.

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(Edit)

Real-world example: EXTJS Fileupload - Problem with IE8 security bar