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Editorial Team
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Asked: 2026-05-13T06:34:41+00:00

I’m developing a front-end to a Rails application. In cross-browser testing, I immediately discovered

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I’m developing a front-end to a Rails application. In cross-browser testing, I immediately discovered that Internet Explorer (apparently all modern versions, but at least IE 7 and IE 8) is not correctly interpreting a file I’m trying to load via AJAX (with jQuery) as JavaScript. A file download warning appears and the user needs to confirm that the file should be downloaded. Unfortunately, this is not acceptable for the purposes of the application.

I created a couple of test files; one is just a JavaScript file served from Amazon S3; the other is actually a resource URL served by Varnish/Rails. The latter is the one that triggers the warning. So:

LINK: URL that gives a warning in IE

REQUEST HEADERS:

Accept:     application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_2; en-us) AppleWebKit/531.21.8 (KHTML, like Gecko) Version/4.0.4 Safari/531.21.10

RESPONSE HEADERS:

Age:              1952
Cache-Control:    public, max-age=3598
Connection:       keep-alive
Content-Encoding: gzip
Content-Length:   2060
Content-Type:     text/javascript; charset=utf-8
Date:             Fri, 13 Nov 2009 22:54:18 GMT
Etag:             "272d9ec2e59aa92da18758cf42a4d729"
Server:           nginx/0.7.61 + Phusion Passenger 2.2.5 (mod_rails/mod_rack)
Status:           200 OK
Via:              1.1 varnish
X-Powered-By:     Phusion Passenger (mod_rails/mod_rack) 2.2.5
X-Runtime:        0.11573
X-Varnish:        176673116 176651738

LINK: URL that does not give a warning in IE

REQUEST HEADERS:

Accept:     application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_2; en-us) AppleWebKit/531.21.8 (KHTML, like Gecko) Version/4.0.4 Safari/531.21.10

RESPONSE HEADERS:

Age:              14
Connection:       keep-alive
Content-Encoding: gzip
Content-Length:   52
Content-Type:     text/javascript
Date:             Fri, 13 Nov 2009 22:55:03 GMT
Etag:             "7b7ded6696ee52551289c856d3173db4"
Last-Modified:    Fri, 13 Nov 2009 22:30:45 GMT
Server:           AmazonS3
Via:              1.1 varnish
X-Amz-Id-2:       CR79uoLC67sr0e0uj4CUOCoBQgcIW/jaJc/FNSA3zsK3Lns/gAqx98/T9h/UeJGm
X-Amz-Request-Id: BCF2F2D69F5126DD
X-Varnish:        1566212056 1566211955

What immediately sticks out to me is the Content-Type of “text/javascript; charset=utf-8” for the URL that gives a warning – is that valid? I had always assumed that only “text/javascript” would be valid.

Also, the URL that gives a warning returns content of Content-Type “text/javascript,” but it is a Rails URL that does not have an extension of .js – could that make a difference?

Is there anything else that sticks out, or does anyone have any other ideas of what could be causing this problem? Thanks very much for any help.

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1 Answer

  1. Editorial Team

    It’s been some time and I’ve since forgotten the details of this problem, but I do know that the ultimate cause was due to a POST request that returned a Content-Type of “text/javascript.”

    Apparently, IE interprets POSTs that return “text/javascript” in the response headers as a security threat, which causes it to display the dreadful, and terribly uninformative, error message bar.

    We changed the Content-Type of the response to “text/html” and that solved it!

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