alert method displays a visual alert box on screen. The alert method parameter is displayed to the user in plain text:
window is the global object, you can call also use the following shorthand:
So what does
window.alert() do? Well, let's take the following example:
alertmethod is technically a property of
windowobject, but since all
windowproperties are automatically global variables, we can use
alertas a global variable instead of as a property of
window- meaning you can directly use
alert acts as a modal prompt meaning that the code calling
alert('Pause!'); console.log('Alert was dismissed');
However the specification actually allows other event-triggered code to continue to execute even though a modal dialog is still being shown. In such implementations, it is possible for other code to run while the modal dialog is being shown.
The use of alerts is usually discouraged in favour of other methods that do not block users from interacting with the page - in order to create a better user experience. Nevertheless, it can be useful for debugging.
Starting with Chrome 46.0,
window.alert() is blocked inside an
<iframe> unless its sandbox attribute has the value allow-modal.