How to Handle Alerts and Dialogs in Vibium

To handle alerts and dialogs in Vibium, register a handler with vibe.on_dialog(handler) before the action that opens the dialog, then call dialog.accept() or dialog.dismiss() inside it. Native browser dialogs — alert(), confirm(), prompt(), and beforeunload — block the page until they are answered, so Vibium surfaces each one as a dialog object passed to your callback. Inside the handler you can read dialog.message() for the text and dialog.type() for the kind of dialog, then respond: dialog.accept() clicks OK (and, for a prompt, you can pass the text to return), while dialog.dismiss() clicks Cancel. Vibium maps these to the WebDriver BiDi browsingContext.userPromptOpened event and handleUserPrompt command under the hood, so behavior is consistent and standards-based. Register the handler first, then trigger the dialog — the callback fires the moment the prompt appears.

How do I accept a JavaScript alert in Vibium?

Register a dialog handler with on_dialog() before you trigger the alert, then accept it inside the callback. The handler must be in place first, because the dialog blocks the page as soon as it opens.

from vibium import browser_sync as browser
 
vibe = browser.launch()
vibe.go("https://example.com")
 
# Register the handler BEFORE the action that opens the dialog.
vibe.on_dialog(lambda dialog: dialog.accept())
 
# This click triggers a window.alert(...) — the handler accepts it.
vibe.find(role="button", text="Show alert").click()
 
vibe.quit()

The lambda dialog: dialog.accept() callback runs automatically when the alert appears, clicking OK so the page unblocks and your script continues. Because the handler is registered up front, you never have to poll for the dialog or guess at timing — Vibium invokes the callback as soon as the prompt opens.

How do I read a dialog's message and type?

Inside the handler, call dialog.message() to read the text and dialog.type() to learn whether it's an alert, confirm, prompt, or beforeunload. This lets you assert on the wording or branch your response.

from vibium import browser_sync as browser
 
vibe = browser.launch()
vibe.go("https://example.com")
 
def handle(dialog):
    print("type:", dialog.type())       # "confirm"
    print("message:", dialog.message())  # "Delete this item?"
    dialog.accept()
 
vibe.on_dialog(handle)
vibe.find(role="button", text="Delete").click()
 
vibe.quit()

A named function (instead of a lambda) is the natural fit once you want to inspect the dialog before responding. You can save dialog.message() to a variable and assert on it, which is handy when a test needs to verify the exact confirmation copy a user would see.

How do I dismiss a confirm or cancel a prompt?

Call dialog.dismiss() to click Cancel. For a confirm() this makes the page see a "false" result; for a prompt() it cancels input entirely so the prompt returns null.

from vibium import browser_sync as browser
 
vibe = browser.launch()
vibe.go("https://example.com")
 
# Dismiss every dialog — useful for declining a "Leave page?" beforeunload.
vibe.on_dialog(lambda dialog: dialog.dismiss())
 
vibe.find(role="button", text="Cancel changes").click()
 
vibe.quit()

Dismissing is the right move when you want to test the "negative" branch — for example, confirming that clicking Cancel on a delete confirmation leaves the row untouched. Pair this with a find() check afterward to assert nothing changed.

How do I answer a prompt dialog with text?

Pass the answer string to accept(). For a prompt() dialog, that string becomes the value JavaScript receives; for alerts and confirms the argument is simply ignored.

from vibium import browser_sync as browser
 
vibe = browser.launch()
vibe.go("https://example.com")
 
# prompt("What's your name?") will receive "Vibium"
vibe.on_dialog(lambda dialog: dialog.accept("Vibium"))
 
vibe.find(role="button", text="Enter name").click()
 
vibe.quit()

This is the only way to supply input to a native prompt, since the dialog is rendered by the browser chrome, not the page DOM — you can't find() and type() into it. Use dialog.accept("text") for prompts and plain dialog.accept() for alerts and confirms.

Why dialogs need a handler, not a find()

Native dialogs live in the browser's UI layer, outside the page's HTML, so locator strategies don't reach them. Vibium routes them through the BiDi userPromptOpened event instead, calling your on_dialog handler the instant a dialog appears. If no handler is registered, Vibium's default behavior keeps your script from hanging — but register one explicitly whenever a click might open a dialog, so you control whether it's accepted or dismissed. To learn how Vibium's BiDi foundation enables this, see What is WebDriver BiDi?.

Next steps

• How to Click Elements in Vibium
• How to Execute JavaScript in Vibium
• What is Vibium?