How to inject javascript into page before page loads with selenium

Question

I'm trying to inject javascript into a page so that it runs before any other scripts are loaded/executed.

I have searched around and seen multiple suggestions saying that this is possible via the Devtool API and calling Page.addScriptToEvaluateOnNewDocument but I can't seem to get it to work.

This is what I have tried:

from selenium import webdriver driver = webdriver.Chrome() driver.get(url) driver.execute_cdp_cmd('Page.addScriptToEvaluateOnNewDocument', {'source': 'alert("This is an alert.")'})

The code runs without any error, but no alert is shown in the browser. What am I missing?

CatChMeIfUCan · Accepted Answer · 2021-08-02 12:09:47Z

2

you should add the code after creating the driver but before you get the web page

from selenium import webdriver driver = webdriver.Chrome() driver.execute_cdp_cmd('Page.addScriptToEvaluateOnNewDocument', {'source': 'alert("This is an alert.")'}) driver.get(url)

answered Aug 2, 2021 at 12:09

CatChMeIfUCan

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2 Comments

stilljake Over a year ago

This throws an error: ``` raise exception_class(message, screen, stacktrace, alert_text) selenium.common.exceptions.UnexpectedAlertPresentException: Alert Text: This is an alert. Message: unexpected alert open: {Alert text : This is an alert.} (Session info: chrome=92.0.4515.107) ```

CatChMeIfUCan Over a year ago

works fine for me! try to accept alert in the code the error disapears

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