Description The alert() method displays an alert box with a message and an OK button. The alert() method is used when you want information to come through to the user.

JavaScript has three kind of popup boxes: Alert box, Confirm box, and Prompt box.

The W3Schools online code editor allows you to edit code and view the result in your browser

Alerts Alert messages can be used to notify the user about something special: danger, success, information or warning.

All global JavaScript objects, functions, and variables automatically become members of the window object. Global variables are properties of the window object.

The window object represents an open window in a browser. If a document contain frames (<iframe> tags), the browser creates one window object for the HTML document, and one additional window object for each frame.

JavaScript Display Possibilities JavaScript can "display" data in different ways: Writing into an HTML element, using innerHTML or innerText. Writing into the HTML output using document.write(). Writing into an alert box, using window.alert(). Writing into the browser console, using console.log().

Example Using onload on an <img> element. Alert "Image is loaded" immediately after an image has been loaded:

The Tryit Editor allows users to experiment with JavaScript code and see the results in real-time.

let text = "Hello World!"; let encoded = window.btoa(text); let decoded = window.atob(encoded);