What is an alert box in JavaScript?

An alert dialog box is mostly used to give a warning message to the users. For example, if one input field requires to enter some text but the user does not provide any input, then as a part of validation, you can use an alert box to give a warning message.

Nonetheless, an alert box can still be used for friendlier messages. Alert box gives only one button "OK" to select and proceed.


You can try to run the following code to learn how to add an alert box −

Live Demo

            function Warn() {
               alert ("This is a warning message!");
               document.write ("This is a warning message!");
      <p>Click the following button to see the result: </p>
         <input type="button" value="Click Me" onclick="Warn();" />