The JavaScript alert is a dialogue box that pops up and takes the focus away from the current window and forces the web browser to read the message. You must have JavaScript enabled on your web browser (but most people do these days). Alerts should be very, very rarely used and only when really needed. So this is definitely a case of "Just because you can, doesn't mean you should."

Possible Uses:

• If you want to be absolutely sure your visitors see a message before doing anything on the website.
• You would like to warn the user about something. For example "the following page contains humor not suitable for those under the age of 14."
• An error has occurred and you want to inform the user of the problem.
• When asking users for confirmation of some action. For example, if a visitor has filled out a form and have just agreed to send you $100 each month for life. You probably want to ask them again if they are absolutely positive they want to go through with this decision!

For Fun:

Just for fun, let's suppose that we are making an alert for your site that asks people to hand over $100 every month. We need to add an alert to be sure these people are in agreement. The following code will add an alert by using an HTML button and the onClick event.

Note: The samples above are simple ones. If you need something a bit more complex, you can do a search for "Javascript Alert Boxes" and can find a lot of examples along with instructions on how to implement them. Also note that an alert box is a function of the operating system, so it cannot be styled with CSS (although there are some jQuery scripts that can make the alert a bit fancier.)