javascript error: circular reference error while trying to retrieve navigator.plugins using Selenium and Python

Question

I'm trying to retrieve the value of navigator.plugins from a Selenium driven ChromeDriver initiated google-chrome Browsing Context.

Using google-chrome-devtools I'm able to retrieve navigator.userAgent and navigator.plugins as follows:

But using Selenium's execute_script() method I'm able to extract the navigator.userAgent but navigator.plugins raises the following circular reference error:

• Code Block:

  from selenium import webdriver 
  
  options = webdriver.ChromeOptions() 
  options.add_argument("start-maximized")
  driver = webdriver.Chrome(options=options, executable_path=r'C:\WebDrivers\chromedriver.exe')
  driver.get("https://www.google.com/")
  print("userAgent: "+driver.execute_script("return navigator.userAgent;"))
  print("plugins: "+driver.execute_script("return navigator.plugins;"))
  

• Console Output:

  userAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36
  Traceback (most recent call last):
    File "C:\Users\Soma Bhattacharjee\Desktop\Debanjan\PyPrograms\navigator_properties.py", line 19, in <module>
      print("vendor: "+driver.execute_script("return navigator.plugins;"))
    File "C:\Python\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 636, in execute_script
      'args': converted_args})['value']
    File "C:\Python\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute
      self.error_handler.check_response(response)
    File "C:\Python\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response
      raise exception_class(message, screen, stacktrace)
  selenium.common.exceptions.JavascriptException: Message: javascript error: circular reference
    (Session info: chrome=83.0.4103.116)
  

I've been through the following discussions on circular reference and I understand the concept. But I am not sure how should I address the issue here.

• Example of a circular reference in Javascript?
• Detecting and fixing circular references in JavaScript
• Is circular reference between objects a bad practice?

Can someone help me to retrieve the navigator.plugins please?

Answer 1

Circular Reference

A circular reference occurs if two separate objects pass references to each other. Circular referencing implies that the 2 objects referencing each other are tightly coupled and changes to one object may need changes in other as well.

---

NavigatorPlugins.plugins

NavigatorPlugins.plugins returns a PluginArray object, listing the Plugin objects describing the plugins installed in the application. plugins is PluginArray object used to access Plugin objects either by name or as a list of items. The returned value has the length property and supports accessing individual items using bracket notation (e.g. plugins[2]), as well as via item(index) and namedItem("name") methods.

---

To extract the navigator.plugins properties you can use the following solutions:

• To get the list of names of the plugins:

  print(driver.execute_script("return Array.from(navigator.plugins).map(({name}) => name);"))
  

  • Console Output:

    ['Chrome PDF Plugin', 'Chrome PDF Viewer', 'Native Client']
    

• To get the list of filename of the plugins:

  print(driver.execute_script("return Array.from(navigator.plugins).map(({filename}) => filename);"))
  

  • Console Output:

    ['internal-pdf-viewer', 'mhjfbmdgcfjbbpaeojofohoefgiehjai', 'internal-nacl-plugin']
    

• To get the list of description of the plugins:

  print(driver.execute_script("return Array.from(navigator.plugins).map(({description}) => description);"))
  

  • Console Output:

    ['Portable Document Format', '', '']
    

Answer 2

There might be a serialization issue when you query a non-primitive data structure from a browser realm. By closely inspecting the hierarchy of a single plugin, we can see it has a recursive structure which is an issue for the serializer.

If you need a list of plugins, try returning just a serialized, newline-separated string and then split it by a newline symbol in the Python realm.

For example:

plugins = driver.execute_script("return Array.from(navigator.plugins).map(({name}) => name).join('\n');").split('\n')

Answer 3

I'm assuming it has something to do with the fact that navigator.plugins returns a PluginArray.

The PluginArray page lists the methods and properties that are available and with that I wrote this code that returns the list of names. You can adapt it to whatever you need.

print("plugins: " + driver.execute_script("var list = [];for(var i = 0; i < navigator.plugins.length; i++) { list.push(navigator.plugins[i].name); }; return list.join();"))