User Notifications and Alerts - Archive of obsolete content
custom alerts creating custom solutions for alerting the user is not complicated, given the advantages of xul overlays and css positioning.

UI - Archive of obsolete content
ated vertical column toolbar including entries and access elements into the toolbar panel a movable, expandable, and custom styled content element to display jetpack content tabs adding events and interacting with browser tabs and their contained documents statusbar low-level functions and basic calls notifications a system for alerting users via provided ui mechanisms selection interacting with user-selected content window mitigates and eases interactions between different browser windows ...

WAI-ARIA basics - Learn web development
this is a fairly trivial example, but just imagine if you were creating a complex ui with lots of constantly updating content, like a chat room, or a strategy game ui, or a live updating shopping cart display — it would be impossible to use the app in any effective way without some kind of way of alerting the user to the updates.

Graceful asynchronous programming with Promises - Learn web development
you could also try doing something else with the resolved message rather than just alerting it.

Introduction to the server side - Learn web development
a web server might send warning messages to site administrators alerting them to low memory on the server, or suspicious user activity.

Introduction to automated testing - Learn web development
use a browser automation system like selenium to run specific tests on installed browsers and return results, alerting you to failures in browsers as they crop up.

Examples
in the example below we try alerting an undefined variable.

nsIRadioInterfaceLayer
speakerenabled bool constants call state constants constant value description call_state_unknown 0 call_state_dialing 1 call_state_alerting 2 call_state_busy 3 call_state_connecting 4 call_state_connected 5 call_state_holding 6 call_state_held 7 call_state_resuming 8 call_state_disconnecting 9 call_state_disconnected 10 call_state_incoming 11 datacall_state_unknown 0 datacall_state_connecting 1 datacall_state_connected 2 datacall_state_disconnecting 3 datacall_state_disconnected ...

Range.toString() - Web APIs
alerting the contents of a range makes an implicit tostring() call, so comparing range and text through an alert dialog is ineffective.

Cognitive accessibility - Accessibility
alerting the user and providing a buffer of at least 20 seconds to extend the timeout duration by a factor of 10 with a simple action, such as hitting the space bar.

Event reference
se events abort blocked complete error success upgradeneeded versionchange script events afterscriptexecute beforescriptexecute menu events dommenuitemactive dommenuiteminactive window events close popup events popuphidden popuphiding popupshowing popupshown tab events visibilitychange battery events chargingchange chargingtimechange dischargingtimechange levelchange call events alerting busy callschanged cfstatechange connecting dialing disconnected disconnecting error held, holding incoming resuming statechange voicechange sensor events compassneedscalibration devicemotion deviceorientation orientationchange smartcard events icccardlockerror iccinfochange smartcard-insert smartcard-remove stkcommand stksessionend cardstatechange sms and ussd events delivered received sent...

PWA developer guide - Progressive web apps (PWAs)
using service workers to run offline description alerting the user using notifications description creating a web app from an existing site description advanced topics pushing data from the server to your web application some description resource management description integration with the host device description security and privacy description gaming topics for web app developers description polishing web apps web api equivalen...