[🐛 Bug]: JavaScript alerts/prompts not displayed or handled when using Chrome with BiDi mode (Selenium 4.38 & .Net v4.8)

[SKumar-777]

Description

When launching Chrome with BiDi enabled using UseWebSocketUrl and --remote-debugging-pipe, JavaScript alert dialogs (e.g., alert(), confirm(), prompt()) are suppressed. The same site displays the dialogs correctly when launched manually or when BiDi mode is disabled.

This issue prevents automation of any site logic that depends on JavaScript dialogs. Is that BiDi mode intentionally suppresses JavaScript dialogs?, If so, this makes it currently impossible to migrate existing Selenium suites to BiDi if they rely on standard alert handling, creating a functional gap between BiDi and legacy WebDriver capabilities.

Note: BiDi mode was enabled intentionally to support loading my Chrome extension in the automated chrome session (v142).

ChromeOptions options = new ChromeOptions();
//Using Bidi to load my chrome exetension in chrome browser v142.
options.UseWebSocketUrl = true;//To enable BiDi protocol for communication.
options.AddArgument("--remote-debugging-pipe");
options.AddArgument("--enable-unsafe-extension-debugging");
options.AddArguments("--no-sandbox");
driver = new RemoteWebDriver(new Uri("http://localhost:xxxx"), options);
//Extension load code ....
driver.Navigate().GoToUrl("https://demo.automationtesting.in/Alerts.html");
// Clicks the button to display a JavaScript alert, but the alert is not displayed (suppressed in BiDi mode).
try
{
IAlert alert = driver.SwitchTo().Alert();
Console.WriteLine("Alert text: " + alert.Text);
alert.SendKeys("Selenium BiDi Test");
alert.Accept();
}
catch (NoAlertPresentException)
{
Console.WriteLine("No alert displayed when using BiDi mode.");
}

Reproducible Code

ChromeOptions options = new ChromeOptions();
//Using Bidi to load my chrome exetension in chrome browser v142.
options.UseWebSocketUrl = true;//To enable BiDi protocol for communication.
options.AddArgument("--remote-debugging-pipe");
options.AddArgument("--enable-unsafe-extension-debugging");
options.AddArguments("--no-sandbox");
driver = new RemoteWebDriver(new Uri("http://localhost:xxxx"), options);
//Extension load code ....
driver.Navigate().GoToUrl("https://demo.automationtesting.in/Alerts.html");
// Clicks the button to display a JavaScript alert, but the alert is not displayed (suppressed in BiDi mode).
try
{
    IAlert alert = driver.SwitchTo().Alert();
    Console.WriteLine("Alert text: " + alert.Text);
    alert.SendKeys("Selenium BiDi Test");
    alert.Accept();
}
catch (NoAlertPresentException)
{
    Console.WriteLine("No alert displayed when using BiDi mode.");
}

[selenium-ci]

@SKumar-777, thank you for creating this issue. We will troubleshoot it as soon as we can.

Selenium Triage Team: remember to follow the Triage Guide

[praveenkumar800]

I’m able to reproduce this issue on my end as well.

This impacting our customer deliverables since several of our automation workflows depend on handling JavaScript dialogs (e.g., alert(), confirm(), prompt()). With BiDi enabled (UseWebSocketUrl = true and --remote-debugging-pipe), these dialogs are suppressed, which prevents us from validating key application logic.

Please let us know if this suppression is an intentional behaviour in BiDi mode or if a fix/workaround is planned.

[cgoldberg]

AFAIK, the default for "unhandledPromptBehavior" in the BiDi spec is "dismiss". I just verified that if you change it to "ignore" for the current browsing context, you do see the prompts on the page you used.

I tested this in Python. Can you verify this works correctly in .NET if it is set to "ignore"?

I think this is functioning correctly.

[SKumar-777]

@cgoldberg - It worked after I set "options.UnhandledPromptBehavior = UnhandledPromptBehavior.Ignore;". Thanks a lot!