index.md

---

title: JavaScript error
slug: Web/WebDriver/Errors/JavaScriptError

---

{{QuickLinksWithSubpages("/en-US/docs/Web/WebDriver/Errors")}}

The JavaScript error is a WebDriver error that occurs when a script the supplied by the user fails to execute.

The underlying cause of the execution error is often supplied in the error message, along with a stacktrace provided by the JavaScript engine in the browser.

Example

Consider the following injected script which tries to use an undefined variable. In JavaScript this normally causes a ReferenceError to be thrown. WebDriver catches this error and serializes it as a JavaScript error:

from selenium import webdriver
from selenium.common import exceptions

session = webdriver.Firefox()
try:
    session.execute_script("return foo")
except exceptions.JavascriptException as e:
    print(e.message)

Output:

JavascriptException: ReferenceError: foo is not defined

See also

• List of WebDriver errors

• Associated commands:

  • Execute Script

  • Execute Async Script