# Main World Execution

By default, all JavaScript execution is ran in an isolated scope, invisible to the page.

This makes it impossible for the page to detect JavaScript reading the DOM:

>>> page.goto("https://example.com/")
>>> page.evaluate("document.querySelector('h1').innerText")
'Example Domain'

However, it will not be able to modify the DOM:

>>> page.evaluate("document.querySelector('h1').remove()")
# Will not work!

To be able to modify the DOM, run JavaScript in the main world—the non-isolated scope.

To enable main world execution, set the main_world_eval parameter to True:

with Camoufox(main_world_eval=True) as browser:
    page = browser.new_page()
    page.goto("https://example.com/")

Now, you can inject JavaScript in the main world by prefixing the code with mw:

>>> page.evaluate("mw:document.querySelector('h1').remove()")
# h1 is now removed!

You can also return JSON serializable data from the main world:

>>> page.evaluate("mw:{key: 'value'}")
{'key': 'value'}