[webkit-dev] Improving DOM Exception console messages.

Wed Sep 26 09:20:54 PDT 2012

Sounds great!

On Wed, Sep 26, 2012 at 8:12 AM, Mike West <mkwst at chromium.org> wrote:

> Hello, webkit-dev!
>
> TL;DR: I'd like to improve the console messages displayed for DOM
> exceptions. I'm hoping that no one thinks this is a miserable,
> miserable idea.
>
> At the moment, the following code generates an exception with a
> message reading "SECURITY_ERR: DOM Exception 18".
>
> ----8<------8<------8<------
> <!doctype html>
> <html>
>   <head>
>     <title>Bug 152212</title>
>     <meta http-equiv="X-WebKit-CSP" content="connect-src 'none'">
>   </head>
>   <body>
>     <script>
>       var xhr = new XMLHttpRequest();
>       var url = '
> https://api.twitter.com/1/trends/daily.json?exclude=hashtags';
>       xhr.open('GET', url, true);
>       xhr.send();
>     </script>
>   </body>
> </html>
> ---->8------>8------>8------
>
> In this case, the exception is generated because Content Security
> Policy blocks the XMLHttpRequest, but it's tough to tell, because the
> exact same error crops up for 31 different exception cases[1]. It
> might be CSP, it might be a disallowed HTTP method, who knows. Because
> of the variety, searching for the exception message is unhelpful. In
> this case, I end up on StackOverflow, reading about cookies and
> jQuery[2], which is unlikely to be of service.
>
> This isn't a great experience, and while SECURITY_ERR is particularly
> widespread, the scenario is similar for the other DOM exceptions
> WebKit throws. Each ends up in ExceptionBase, where a message is
> assembled from the exception type and code, and the developer is left
> more than a little underinformed.
>
> I'd like to add the ability to pass some sort of contextual message
> along with the error code. This would involve some work on JSC and V8
> bindings, as well as a whole lot of single-line changes to the various
> bits of the DOM where these error codes are generated.
>
> In this case, a useful message might be: "SECURITY_ERR: DOM Exception
> 18. XMLHttpRequest connections to
> 'http://localhost:8000/xmlhttprequest/resources/get.txt' are blocked
> due to this page's Content Security Policy." This would have the
> positive impact of giving developers something useful to work with. It
> would also have the impact of changing the exception text, which is
> why I'm writing this email. :)
>
> Before I get too far along in experimental implementations, are there
> fundamental objections to changing the exception text to include some
> optional context?
>
> [1]:
> https://cs.corp.google.com/#search/&q=SECURITY_ERR%20file:WebCore&sq=package:%5Echrome$&type=cs
> [2]:
> http://stackoverflow.com/questions/2704929/uncaught-error-security-err-dom-exception-18
>
> -Mike
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> webkit-dev at lists.webkit.org
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>
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