JavaScript: The Definitive Guide, 6th Edition

Dialog Boxes

The Window object provides three methods for displaying simple dialog boxes to the user. alert() displays a message to the user and waits for the user to dismiss the dialog. confirm() displays a message, waits for the user to click an OK or Cancel button and returns a boolean value. And prompt() displays a message, waits for the user to enter a string, and returns that string. The following code uses all three methods:

do {
    var name = prompt("What is your name?");                  // Get a string
    var correct = confirm("You entered '" + name + "'.\n" +   // Get a boolean
                          "Click Okay to proceed or Cancel to re-enter.");
} while(!correct)
alert("Hello, " + name);  // Display a plain message

Although the alert(), confirm(), and prompt() methods are very easy to use, good design dictates that you use them sparingly, if at all. Dialog boxes like these are not a common feature on the Web, and most users will find the dialog boxes produced by these methods disruptive to their browsing experience. The only common use for these methods today is debugging: JavaScript programmers sometimes insert alert() methods in code that is not working in an attempt to diagnose the problem.

Note that the messages displayed by alert(), confirm(), and prompt() are plain text, not HTML-formatted text. You can format these dialog boxes only with spaces, newlines, and punctuation characters.

The confirm() and prompt() methods block—that is, these methods do not return until the user dismisses the dialog boxes they display. ...