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Java Script prompt Message Box

By Stephen Bucaro

In Java Script programming, there are many occasions when you need to display a short message to the user, or request a bit of information from the user. In these instances, you can use a message box.

Java Script provides three types of message boxes, the alert, confirm, and prompt. They are all easy to create and use.

• These message boxes are "modal" dialog boxes, meaning that program flow halts while the message box is visible. The user is unable to use the page that spawned the message box until they click on a button to close the message box. This may be disruptive to the user. You can also design your own custom message box, which you may or may not choose to make modal.

Prompt message box

A prompt presents a message, a text box for user input, an [OK] button and a [Cancel] button. If the user enters a response in the text box and clicks on the [OK] button, the prompt returns the users response. If the user clicks on the [cancel] button, whether the user enters a response in the text box or not, the prompt returns null. Clicking on either button dismisses the dialog box. Example code to create a prompt message box is shown below.

var response = prompt("Message")

if(response != null)
{
  alert(response);
}
else
{
  alert("No input");
}

You can supply a default response. If the default response is acceptable to the user, they can just click on the [OK] button.

prompt("Message","Default Response");

If you don't supply a default response, the text "undefined" will appear in the input text box and, if the user clicks on the [OK] button without entering a response in the text box, the prompt will return undefined.

If you don't have a specific default response, but you don't want "undefined" to appear in the text box, provide an empty string as the default response, as shown below.

var response = prompt("message","")

if(response != null && response != "")
{
  alert(response);
}
else
{
  alert("No input");
}

• If you're prompting the user for a numerical input, don't forget to use the isNaN function along with parseInt or parseFloat to convert the string input value to a number.

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