I'm trying to set MutationObserver for observing page mutation while loading.
In order to do that, MutationObserver should be configured before page loading.
With selenium-chromedriver, couldn't find the way to inject JS for such purpose.
I know chrome extension can do that but extensions won't work on headless mode.
That's the problem.
It's possible via the DevTool API by calling Page.addScriptToEvaluateOnNewDocument
from selenium import webdriver from selenium.webdriver.remote.webdriver import WebDriver import json def send(driver, cmd, params={}): resource = "/session/%s/chromium/send_command_and_get_result" % driver.session_id url = driver.command_executor._url + resource body = json.dumps({'cmd': cmd, 'params': params}) response = driver.command_executor._request('POST', url, body) if response['status']: raise Exception(response.get('value')) return response.get('value') def add_script(driver, script): send(driver, "Page.addScriptToEvaluateOnNewDocument", {"source": script}) WebDriver.add_script = add_script # launch Chrome driver = webdriver.Chrome() # add a script which will be executed when the page starts loading driver.add_script(""" if (window.self === window.top) { // if main document console.log('add script'); } """) # load a page driver.get("https://stackoverflow.com/questions") 
execute_cdp_cmd?We can now use execute_cdp_cmd(cmd, cmd_args) to execute Chrome Devtools Protocol command in Selenium
from selenium import webdriver driver = webdriver.Chrome() driver.execute_cdp_cmd( "Page.addScriptToEvaluateOnNewDocument", { "source": """// Your JavaScript here""" } ) driver.get("https://stackoverflow.com") driver.quit() The argument for "source" is just a string. So you can actually write your script in a .js file (for syntax highlighting) and read it using Python
