Javascript close alert box

no control over the dialog box, if you had control over the dialog box you could write obtrusive javascript code. (Its is not a good idea to use alert for anything except debugging)

Appears you can somewhat accomplish something similar with the Notification API. You can't control how long it stays visible (probably an OS preference of some kind--unless you specify requireInteraction true, then it stays up forever or until dismissed or until you close it), and it requires the user to click "allow notifications" (unfortunately) first, but here it is:

If you want it to close after 1s (all OS's leave it open 1s at least):

var notification = new Notification("Hi there!", {body: "some text"});
setTimeout(function() {notification.close()}, 1000);

If you wanted to show it longer than the "default" you could bind to the onclose callback and show another repeat notification I suppose, to replace it.

Ref: inspired by this answer, though that answer doesn't work in modern Chrome anymore, but the Notification API does.

As mentioned previously you really can't do this. You can do a modal dialog inside the window using a UI framework, or you can have a popup window, with a script that auto-closes after a timeout... each has a negative aspect. The modal window inside the browser won't create any notification if the window is minimized, and a programmatic (timer based) popup is likely to be blocked by modern browsers, and popup blockers.