Javascript window.alert()

The alert method displays a visual alert box on screen. The alert method parameter is displayed to the user in plain text:

window.alert(message);

Because window is the global object, you can call also use the following shorthand:

alert(message);

let's take the following example:

alert('hello, world');

Output

Alert Message

The alert method is technically a property of window object, but since all window properties are
automatically global variables, we can use alert as a global variable instead of as a property of window -
meaning you can directly use alert() instead of window.alert().

Unlike using console.log, alert acts as a modal prompt meaning that the code calling alert will pause until the
prompt is answered. Traditionally this means that no other JavaScript code will execute until the alert is dismissed:

alert('Pause!');
console.log('Alert was dismissed');

However the specification actually allows other event-triggered code to continue to execute even though a modaldialog is still being shown. In such implementations, it is possible for other code to run while the modal dialog is being shown.

More information about usage of the alert method can be found in the modals prompts topic.

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.