A Brief Look at JavaScript - Web Development and Design Foundations with XHTML

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In-Depth Information

Here's an example of a function definition:

function showAlerts()

{

alert("Please click OK to continue.");

alert("Please click OK again.");

alert("Click OK for the last time to continue.");

}

The function can be called using the following statement:

showAlerts();

Now, we could include the showAlerts() function call in a button as follows:

<input type="button" value="click to see alerts"

onclick="showAlerts();" />

When the user clicks the button, the showAlerts() function will be called, and the

three alert messages will appear, one after the other. Typically, function definitions are

placed in the <head> area of the XHTML document. This loads the function definition

code but it does not execute until it is called. This ensures that the function definition is

loaded and ready to use before the function is called.

HANDS-ON PRACTICE 14.7

In this Hands-On Practice you will edit the quantityif.html document to move the

prompting script into a function and call it with an onclick event handler.

Edit the quantityif.html document as follows. There are a few things to note. The script

has been moved into the <head> area and included in a function definition. The

document.write() methods have been changed to alert() methods and the messages

have been altered slightly. The document.write() methods will not work well after the

page has already been written, as is the case in this exercise. Also, there have been some

comments added to the end brackets for the if statement and the function definition.

These comments can help you keep track of the code blocks within the script. The

indentation of the code blocks also helps to identify which brackets begin and end

various statements.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<title>JavaScript Practice</title>

<!-- <![CDATA[

function promptQuantity()

{

var quantity;

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