Window: alert() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

window.alert() instructs the browser to display a dialog with an optional message, and to wait until the user dismisses the dialog.

Under some conditions — for example, when the user switches tabs — the browser may not actually display a dialog, or may not wait for the user to dismiss the dialog.

Syntax

js
alert()
alert(message)

Parameters

message Optional

A string you want to display in the alert dialog, or, alternatively, an object that is converted into a string and displayed.

Return value

None (undefined).

Examples

js
window.alert("Hello world!");
alert("Hello world!");

Both produce:

Black alert dialog box. At the top left small circle icon follow by white open and close square brackets containing this white text: JavaScript application. Below on the left, a Hello world! white text. And on the bottom right a small blue button. The button's text is: ok in black.

Notes

The alert dialog should be used for messages which do not require any response on the part of the user, other than the acknowledgement of the message.

Dialog boxes are modal windows - they prevent the user from accessing the rest of the program's interface until the dialog box is closed. For this reason, you should not overuse any function that creates a dialog box (or modal window).

Alternatively <dialog> element can be used to display alerts.

Specifications

Specification
HTML Standard
# dom-alert-dev

Browser compatibility

BCD tables only load in the browser

See also