Empty Charsets in IE 9 Causing JSON Parsing Errors

My last post was a bit of a pulpy, prosey trope about a problem I had debugging an issue in IE 9. It was supposed to be a fun read - but it turns out I might have actually uncovered an issue with IE 9... so giving the team due respect, here's a bit more detail.

The Spec

The core of the issue here is that IE 9 is strict. Very strict. And that's generally a good thing - unless the spec is a bit too vague. My problem yesterday had to do with the spec, specifically the charset setting of the Content Type:

Is this wrong? You tell me - here's the spec:

The question is this: is the charset null? Or is it invalid?

Reproduction

You can reproduce this quite easily using .NET. You'll need two pages - index.cshtml:

Hi Everyone
Output from JSON:

And then "json.cshtml":

@{
    Response.ContentType = "application/json; charset=";
}
{"message":"Charset Issue"}

You can do this in Rails by setting "content_type" of render manually:

render :json => {:message => "hello there"}.to_json, :content_type => "application/json, charset="

Load the page up in Chrome, Safari, or Firefox and it works. Load it up in IE 9 and you'll get an alert with a very, very weird error:

Thanks Jon!

Credit for this find goes to Jon Galloway who read the spec after I called him names on Twitter :). He found some inconsistent behavior with IE with his reading of the spec (mine too) and has forwarded it off to the IE 9 team.

When I wrote my post yesterday - it was with the understanding that it was my fault :) - but it occurred to me that if it wasn't my fault, then I probably went about things a bit poorly. So hopefully this post is helpful.

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