browser-use--browser-harness/interaction-skills/dialogs.md

Dialogs

Browser dialogs (alert, confirm, prompt, beforeunload) freeze the JS thread. Two approaches depending on timing.

Detection

page_info() auto-surfaces any open dialog: if one is pending it returns {"dialog": {"type", "message", ...}} instead of the usual viewport dict (because the page's JS is frozen anyway). So if you call page_info() after an action and see a dialog key, handle it before doing anything else.

Reactive: dismiss via CDP (preferred)

Works even when JS is frozen. Handles all dialog types including beforeunload.

# Dismiss and read the message
cdp("Page.handleJavaScriptDialog", accept=True)   # accept / click OK
cdp("Page.handleJavaScriptDialog", accept=False)  # cancel / click Cancel

# Read what the dialog said (from buffered CDP events)
events = drain_events()
for e in events:
    if e["method"] == "Page.javascriptDialogOpening":
        print(e["params"]["type"])     # "alert", "confirm", "prompt", "beforeunload"
        print(e["params"]["message"])  # the dialog text

Undetectable by antibot — no JS injected into the page.

Proactive: stub via JS

Prevents dialogs from ever appearing. Good when you expect multiple alert()/confirm() calls in sequence.

js("""
window.__dialogs__=[];
window.alert=m=>window.__dialogs__.push(String(m));
window.confirm=m=>{window.__dialogs__.push(String(m));return true;};
window.prompt=(m,d)=>{window.__dialogs__.push(String(m));return d||'';};
""")
# ... do actions that trigger dialogs ...
msgs = js("window.__dialogs__||[]")

Tradeoffs:

• Stubs are lost on page navigation -- must re-run the snippet
• confirm() always returns true (auto-approves)
• Detectable by antibot (window.alert.toString() reveals non-native code)
• Does NOT handle beforeunload

beforeunload specifically

Fires when navigating away from a page with unsaved changes (forms, editors, upload pages). The page freezes until the user clicks Leave/Stay.

# Option A: dismiss after navigating (CDP-level, safe)
goto_url("https://new-url.com")
try:
    cdp("Page.handleJavaScriptDialog", accept=True)  # click "Leave"
except:
    pass  # no dialog — normal

# Option B: prevent before navigating (JS injection, detectable)
js("window.onbeforeunload=null")
goto_url("https://new-url.com")