I want to add that it fails sometimes, not always. So it seems to be some kind of timing
problem. Adding a Thread.sleep() or fluentWait seems to help, but we are not completely
sure.

This issue was fixed in r16079 and should be fixed for 2.21

I think this is actually a race-condition between our detection logic and the window
painting - can you update as to whether 2.21 fixes this, when it's released?

2.21 is available

This is still happening for me with 2.21. For now, my workaround is to sleep a bit before
accepting the alert

Still happening using 2.22.0.

I am also seeing this issue with 2.23.1.  In the following code:

} else if (action.equalsIgnoreCase("continue")) {
    driver.switchTo().alert().accept();
        return "pass";

The 'continue' text is successfully detected, but the accept() method is failing with:

Caused by: org.openqa.selenium.WebDriverException: a.document.getElementsByTagName("dialog")[0]
is undefined

So, it appears WebDriver has detected the correct window and can read text.

- Chris

I should mention that this is not an issue on Ubuntu 10.04.  We only see this on Windows
7 and it is regular, but not constant.  It is more likely to occur when running many
tests before this one.  When I run this test in isolation on Windows 7, it typically
runs successfully.

I don't think this is a Windows issue only. I am seeing this error on unix (fc13) using
selenium 2.24.1 as well.

Also getting this in 2.24.1.
This throws the same exception (sometimes):

Alert alert = null;
Wait<WebDriver> wait = new WebDriverWait(driver, 10, 50);
try {
   alert = wait.until(ExpectedConditions.alertIsPresent());
} catch (TimeoutException ignored) {
}
if (alert != null) {
   alert.accept(); // this line throws the exception
}

I am also seeing this issue on windows xp and chrome using latest webdriver 2.24.1

Am also seeing this issues when using FirefoxDriver.

We also get random failures on Windows 7 and Chrome using Selenium 2.25. We tried pretty
much everything that was suggested on forums and nothing seems to fix it.

Any idea on what is going on?

Same behaviour here (W7, FF3.6, WebDriver 2.25)

Same behaviour here (W7, FF16, WebDriver 2.29)

We also get random failures on Windows 2008 and FireFox using Selenium 2.25.

@16, you've updated Selenium and verified it also happens on v2.3.1, *right*? What version
of Firefox?

@17 , no, I have not tried 2.31, I am using 2.25. I'll try 2.31 later.
For my particular case, I don't think the version of FireFox matter, because my local
machine(win7) and my CI build machine(win2008) are using the same version of FireFox.
And it only happens on Windows 2008.

Windows 2008 and FireFox 17 using Selenium 2.31

Getting similar error: a.document.getElementsByTagName(...)[0] is undefined Command.

We see this with Selenium 2.31 on Ubuntu with Firefox 14

Windows xp and Firefox 17 with Selenium2.28

It happens for few times when accept confirmation pop up: a.document.getElementsByTagName(...)[0]
is undefined

Also observed in 2.33

Seeing this on the latest version of Firefox and Windows Server 2008, selenium server
2.33.

Same problem on Windows Server 2012 and selenium 2.33

Same problem with Windows server 2008 and selenium 2.33

The same error occurs randomly on invoking Alert.dismiss().

Code :-

WebDriverWait wait = new WebDriverWait(webDriver, timeout);
Alert alert = wait.until(ExpectedConditions.alertIsPresent());

alert.dismiss();

The same problem on Windows 7, Webdriver 2.35.0.

Same problem Windows 7, Webdriver 2.35.0

As a workaround I wrapped accept call in a try catch and looped until it was successful:

    public void clickOkOnAlertDialog(String dialogText) {

        Sync sync = Sync.start(20);
        while (sync.continueWaiting()) {
            wait = new WebDriverWait(driver, pageTimeoutInSeconds);
            wait.until(ExpectedConditions.alertIsPresent());
            Alert statusConfirm = driver.switchTo().alert();
            junit.framework.Assert.assertEquals(dialogText, statusConfirm.getText());
            try {
                statusConfirm.accept();
                return;
            } catch (WebDriverException e) {
                sync.sleep(250);
            }
        }
        throw new TimeoutException("Unable to locate and dismiss alert dialog: " +
dialogText);
    }

Also the same problem here on Windows Server 2008 Firefox 17.0.9 with Selenium 2.37.0.

I also just randomly saw this error on 64 bit Win 7, Selenium 2.39.0, FF 26.0.

Specifically, I got the following exception when trying to accept an alert:
  ...
  File "C:\Python275\lib\site-packages\selenium-2.39.0-py2.7.egg\selenium\webdriver\common\alert.py",
line 78, in accept
    self.driver.execute(Command.ACCEPT_ALERT)
  File "C:\Python275\lib\site-packages\selenium-2.39.0-py2.7.egg\selenium\webdriver\remote\webdriver.py",
line 164, in execute
    self.error_handler.check_response(response)
  File "C:\Python275\lib\site-packages\selenium-2.39.0-py2.7.egg\selenium\webdriver\remote\errorhandler.py",
line 164, in check_response
    raise exception_class(message, screen, stacktrace)
WebDriverException: Message: u'a.document.getElementsByTagName(...)[0] is undefined'
; Stacktrace: 
    at fxdriver.modals.findButton_ (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:8412)
    at fxdriver.modals.acceptAlert (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:8383)
    at FirefoxDriver.prototype.acceptAlert/< (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:9085)
    at fxdriver.modals.isModalPresent/< (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:8376)
    at fxdriver.Timer.prototype.runWhenTrue/g (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:402)
    at fxdriver.Timer.prototype.runWhenTrue (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:404)
    at fxdriver.modals.isModalPresent (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:8377)
    at FirefoxDriver.prototype.acceptAlert (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/driver_component.js:9087)
    at DelayedCommand.prototype.executeInternal_/h (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/command_processor.js:10831)
    at DelayedCommand.prototype.executeInternal_ (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/command_processor.js:10836)
    at DelayedCommand.prototype.execute/< (file:///c:/users/bfs/appdata/local/temp/tmpyzdwy_/extensions/fxdriver@googlecode.com/components/command_processor.js:10778)

If you run selenium-webdriver app in console, make sure that the browser window that
appears after the app starts does NOT have focus. You can for example click on your
console window as soon as the browser window appears. This should do it:)

If you do not run in console, still, make sure browser window is out of focus.

It core problem and it is present in current last version 2.42.2 of selenium
It happens mostly on slow machines and on pages with heavy JavaScript
The user side solution - wait for some time for element like here http://code.google.com/p/selenium/issues/detail?id=3544#c29
But would be nice to fix this problem by adding timeout attribute in the core

Can some one post a solution code .

I have the same issue JavaScript Error: "e is null , when I run my test now, which
were running fine yesterday.

I have 3 tests in the same class specified by @test. If I comment out any one test,
the other 2 runs fine.

I am not sure how to solve this issue. Can someone help me.

can anybody found a solution for this,any help appreciated

Would love to see this finally fixed too!

Is there a reproduction scenario and page to debug the issue?

Seeing this problem intermittently in Firefox on slower Windows Server 2008 R2 machine
against an Angular JS application, but not on faster Mac and Windows systems. In previous
versions of Selenium, we used the workaround of catching WebDriverException on alert.accept()
and .dismiss() and retrying until a timeout is reached. On 2.42.2 with FirefoxDriver
Java driver and Firefox 31.0, the .accept() and .dismiss() just hang. I have to manually
close the browser window which results in it finally coming back with an UnreachableBrowserException.
I will also say that it always fails in a particular part of the test where it is testing
various error conditions, each resulting in an alert(), between entering data in a
form and clicking a submit button. It almost always hangs on the 5th alert in my case.

I get this:

AssertionError: WebDriverException: Message: u'[JavaScript Error: "e is null" {file:
"file:///tmp/tmp8LbDqE/webdriver-py-profilecopy/extensions/fxdriver@googlecode.com/components/command_processor.js"
line: 7716}]\'[JavaScript Error: "e is null" {file: "file:///tmp/tmp8LbDqE/webdriver-py-profilecopy/extensions/fxdriver@googlecode.com/components/command_processor.js"
line: 7716}]\' when calling method: [nsICommandProcessor::execute]'

always - I use robot framework. Test are executed on Ubuntu and Firefox.

Getting this failure on Windows 8.1 and Firefox ESR 31.0:

Caused by: org.openqa.selenium.remote.ErrorHandler$UnknownServerException: [JavaScript
Error: "a.document.getElementsByTagName(...)[0].getButton is not a function" {file:
"file:///C:/Users/dwray/AppData/Local/Temp/anonymous6976981321126831255webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js"
line: 8120}]'[JavaScript Error: "a.document.getElementsByTagName(...)[0].getButton
is not a function" {file: "file:///C:/Users/dwray/AppData/Local/Temp/anonymous6976981321126831255webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js"
line: 8120}]' when calling method: [nsICommandProcessor::execute]
Build info: version: '2.42.2', revision: '6a6995d31c7c56c340d6f45a76976d43506cd6cc',
time: '2014-06-03 10:52:47'
System info: host: 'T530-1273-DW', ip: '192.168.241.90', os.name: 'Windows 8', os.arch:
'amd64', os.version: '6.2', java.version: '1.7.0_25'

Would love to hear of a work-around.

Does anyone have a succesfull workaroud to this problem?

I'm facing the same Exception using Windows 2008 server and Firefox, and the page I'm
browsing don't have Alerts.

Thanks in advance.

Also as I. On my website also does not have any dialogs, alerts and so on (# 39). And
it completely stopped my work with the tests:/ 

*** Versions

Selenium version: 2.43.0
Browser: Firefox 31.2.0
OS: Debian testing up to date as of 2014/10/17

** What steps will reproduce the problem?

1. Download the `issue.py` file. It reproduces the problem 100% of the time here.

2. Edit it so that the Firefox binary used is 31.2.0.

3. Run it:

    python ./issue.py

** What is the expected output?

No exceptions.

** What do you see instead?

Traceback (most recent call last):
  File "issue.py", line 14, in <module>
    driver.delete_all_cookies()
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py",
line 587, in delete_all_cookies
    self.execute(Command.DELETE_ALL_COOKIES)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py",
line 173, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/errorhandler.py",
line 166, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.WebDriverException: Message: u'[JavaScript Error: "a.document.getElementsByTagName(...)[0].getButton
is not a function" {file: "file:///tmp/tmpgauKk4/extensions/fxdriver@googlecode.com/components/command-processor.js"
line: 8877}]\'[JavaScript Error: "a.document.getElementsByTagName(...)[0].getButton
is not a function" {file: "file:///tmp/tmpgauKk4/extensions/fxdriver@googlecode.com/components/command-processor.js"
line: 8877}]\' when calling method: [nsICommandProcessor::execute]'

** Observations

Only able to reproduce it with FF 31.2.0.

The timing is very sensitive. Without `setTimeout` Selenium detects the alert properly.
It does not take much of an increase beyond 1 to cause the test to avoid the exception.

I believe this error is related to: https://code.google.com/p/selenium/issues/detail?id=7977

This issue was closed by revision 38e8a90463c4.

alert.accept(); is not working in the current version

I'm facing same issue , let's hope it gets fixed in next version of Selenium WebDriver.

Any updates on this issue please...

I'm also looking for an update on this ideally.  I am running into this issue.

i solved this issue by adding time.sleep for few seconds. and this also helps when Selenium
randomly does not find some element on page.