API for checking for JavaScript errors on the page

[lukeis]

Originally reported on Google Code with ID 148

Sometimes a test passes but a browser reports an error on the page.
From a developer's perspective the code is broken because the error
shouldn't have appeared. 

I would like to be able to check if the browser indicates that an error
occured when processing JavaScript.

Reported by adam.dziendziel on 2009-02-07 13:10:18

[lukeis]

Can you please provide more information with a simple example? Thanks!

Reported by dharani@google.com on 2011-01-20 23:24:35

• Labels added: Type-Enhancement
• Labels removed: Type-Defect

[lukeis]

It would be really useful to have a method to check if there were any javascript errors
when loading a page.  It would still be useful even if this was available in only one
of the supported browsers.

Reported by scytacki@concord.org on 2011-04-01 16:55:22

[lukeis]

+1 for this feature. Would be nice to have a annotation like @FailOnJSError or somthing
like that. 

As a workaround, you can define a custom error handler (window.onerror) which pushes
the errors to a global array. In your tests, you can use the javascript execution functions
to check that array for errors.

Reported by christoph.neuroth on 2011-05-03 08:31:02

[lukeis]

+1 for this. Of course it is possible to execute window.onerror but in any case have
this feature build-in Webdriver API will be great.

Reported by slava.markovski on 2011-07-06 22:04:48

[lukeis]

I also have same requirent as mentioned in this issue .As mentioned , I added 

((JavascriptExecutor)driver).executeScript("window.onerror=function(msg, url, linenumber){
   var logerror='Error message: ' + msg + '. Url: ' + url + 'Line Number: ' + linenumber
;   alert(logerror);  return true; }");

into my Selenium script , But I dont get any alert , instead app page hangs due to
JS error ! 

Can you please let me know if my approach is correct ? 

-Anjali

Reported by juhi08 on 2011-07-08 10:55:14

[lukeis]

I used such simple workaround with Firefox 5.0 and Selenium 2.0rc3 and it worked just
fine:

    public static Object execJavaScript(String code) {
        JavascriptExecutor js = (JavascriptExecutor) driver;
        Object result =  js.executeScript(code);
        return result;
    };

In beforeClass:

execJavaScript("window.onerror=function(msg){window.err=msg};");

public void afterMethod(Method m){
    String method_name = m.getName();
    Object result = execJavaScript("var tmp = window.err;window.err=''; return tmp;");
    if (result != null) {
        String res = result.toString(); 
        if (res.length()>0)
            Assert.fail("JS Error in " + method_name + "(): " + res);
    }
};

Buf after upgrading to Firefox 6.0 and Selenium 2.4 it stopped working though it still
works with IE8. Now I cannot find any way to check for JS script errors and it makes
a lot of tests useless. It would be very nice if API could have methods to check JS
errors. Also if you know some workaround for Firefox 6.0 please let me know. 

Thank you. Andrey.

Reported by anikolaev@productengine.com on 2011-08-30 14:59:57

[lukeis]

Injecting window.onerror is not the solution: it allows to capture some errors but not
all (it is difficult to inject it in each window and it can't be done early enough).

I've written a small Firefox extension that registers the JavaScript errors and make
them available in each window what allows to easily retrieve them from WebDriver. It's
open source and available at [1]. I've blogged about it too [2].

@WebDriver Members
are you interested in adding such a feature to WebDriver? I'm open to contribute what
I've done so far and I think that it wouldn't be difficult to add the same support
for HtmlUnit and Chrome. No idea what concerns the other browsers. If yes, it would
be interesting to start a discussion concerning the needed API.

[1] https://github.com/mguillem/JSErrorCollector
[2] http://mguillem.wordpress.com/2011/10/11/webdriver-capture-js-errors-while-running-tests/

Reported by mguillemot@yahoo.fr on 2011-10-11 09:17:34

[lukeis]

Marc: Can you send an email to selenium-developers with your proposed API, what capabilities
it adds, what it requires from the browser, and its limitations? That would be a good
forum to have this discussion :)

Reported by dawagner on 2011-10-11 10:45:03

[lukeis]

@Daniel: done but my post is probably waiting for moderator's approval

Reported by mguillemot@yahoo.fr on 2011-10-12 07:26:16