Capturing JavaScript error in Selenium

Question

Is there a way to capture errors occurring in the DOM in Selenium and probably flag the same as an error in the page?

To give a brief exam

Answer 1

I use the following TestCase.tearDown() in my Python Selenium tests that makes the test fail in case of JavaScript errors:

def tearDown(self):
    browser_logs = driver.get_log("browser")
    errors = [logentry['message'] for logentry in browser_logs if logentry['level'] == 'SEVERE']
    if errors:
        self.fail(f'The following JavaScript errors occurred: {"; ".join(errors)}')

This is inspired by @kleptog and @d3ming answers.

Answer 2

Solution with "window.onerror" didn't work for me.

So I'd like to point out another solution with altering user-extensions.js which helped me:
Can Selenium detect if the page has JavaScript errors?

Main advantage: You don't have to change the page source to do the check.

And here is how to use user-extensions.js:
Using User-Extensions With Selenium-IDE

Note: This solution works only with Firefox

Answer 3

Not sure when this changed, but right now this works for me in Python. The file is a simple page with a javascript error.

In [11]: driver.get("file:///tmp/a.html")

In [12]: driver.get_log("browser")
Out[12]: 
[{u'level': u'SEVERE',
  u'message': u'ReferenceError: foo is not defined',
  u'timestamp': 1450769357488,
  u'type': u''},
 {u'level': u'INFO',
  u'message': u'The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must be declared in the document or in the transfer protocol.',
  u'timestamp': 1450769357498,
  u'type': u''}]

Python-Selenium version 2.48.0 Linux Firefox 43.0

Answer 4

Here's the python webdriver solution I use:

def check_browser_errors(driver):
    """
    Checks browser for errors, returns a list of errors
    :param driver:
    :return:
    """
    try:
        browserlogs = driver.get_log('browser')
    except (ValueError, WebDriverException) as e:
        # Some browsers does not support getting logs
        LOGGER.debug("Could not get browser logs for driver %s due to exception: %s",
                     driver, e)
        return []

    errors = []
    for entry in browserlogs:
        if entry['level'] == 'SEVERE':
            errors.append(entry)
    return errors

Answer 5

Non-window.onerror-based solution (I did not try): http://sejq.blogspot.com/2008/12/can-selenium-detect-if-page-has.html

Answer 6

Here my solution inspiring by jhanifen's response:

// common.js - js file common to the entire app
globalError = []
window.onerror = function (msg, url, line, col, error) {
    globalError.push({msg:msg, url:url, line:line})
};

# tests.py
def tearDown(driver):
    # assert on js error 
    ret = driver.selenium.execute_script("return globalError ")
    driver.assertFalse(ret, "errors %r " % ret)
    # ret will be a dict looking like 
    # {'line': 50, 'url': 'http://localhost:8081/static/js/common.js', 'msg': 'Uncaught ReferenceError: s is not defined'}