Inject javascript fetch and XHR into Selenium with Python

Question

There are several ways to scrape information from websites. Recently I've heard that you can open a selenium webdriver and inject JS on it to fetch specific url from within the website or to replicate AJAX calls.

For example

driver.execute_script("return fetch('www.yoururlhere')")

So, I have a couple of questions regarding it

1 - How do you actually fetch the answer? Inspecting the driver I can see the call but neither in the frontpage nor doing driver.page_source am I able to retrieve it.

2 - How would one replicate more complex requests calls where there is params or data?

requests.get(url=url,headers=headers,params=params)
requests.post(url=url,headers=headers, data=json.loads(data))

How does this work?

Thanks!