How can I determine the mime-type of a document using javascript only?

Question

I need to determine the mime-type of certain files that get returned from the service, I do not know their file extensions or what their type is before hand, basically we retrieve documents from the API like such: "http://site.com/getFile/BFD843DFLKXJDF" where the random text at the end is some file.

<input type="button" value="Click Me" onClick="alert(document.getElementById('iframeID').contentDocument.contentType);">

<iframe id="iframeID" src="http://site.com/getFile/BFD843DFLKXJDF" width="600" height="600" />

This works in Firefox, it returns in the alert dialog: "application/pdf" for pdf files. However Internet Explorer is the main browser I need to target, "contentDocument" is not defined (apparently I use just "document" instead), but "contentType" is also undefined and I don't know what the IE equivalent would be (google searches have not yielded any results).

Help is greatly appreciated, thanks.

Answer 1

If http://site.com is different than your domain, you won't be able to access its data on any browser. This is because of Cross-site scripting security measures.

Answer 2

Perhaps:

var frame = document.getElementById('iframeID');
var type;

if (frame.contentDocument)
type = frame.contentDocument.contentType;
else
type = frame.contentWindow.document.contentType;
alert(type);

Sorry end of day no time to test....

Answer 3

IE supports document.mimeType, but it seems to give a friendly name not the actual foo/bar syntax. Which is wierd. Though this may be good enough for your purposes.

I don't know why it isn't documented here, but the native IHTMLDocument2 interface does document it here. Very strange.