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

HTML and CSS Reference

In-Depth Information

FAQ

What can I do when my JavaScript code doesn't seem to be working?

You can try the following debugging techniques:

● Open the Error Console in Firefox to see if there are any errors. Common errors include

missing a semicolon at the end of a line, and typing errors in commands.

● Use alert() to print variables to verify the contents. For instance, if you have a variable

named quantity, try alert(quantity); to see what is contained in the variable.

● Ask a classmate to look at your code. It's difficult to edit your own code because you tend

to see what you think you wrote rather than what you actually wrote. It's easier to edit

someone else's code.

● Try to explain your code to a classmate. Often, talking through the code will help you

uncover errors.

● Verify that you are not using any JavaScript reserved words as variable names or function

names. See http://www.webreference.com/javascript/reference/core_ref for a list of

reserved words.

HANDS-ON PRACTICE 14.6

In this Hands-On Practice you will code the quantity example described earlier. The

user will be prompted for a quantity and must enter a quantity greater than 0. We will

assume that the user will enter a number. If the user enters a value of 0 or a negative

number, there will be an error message displayed. If the user enters a value greater than

0, a message will be displayed thanking the user for the order. To stay focused on this

task, we will use a prompt and will write messages to the document.

Open a text editor and enter the following. Notice that there are no semicolon charac-

ters ( ; ) after the brackets:

<!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>

</head>

<body>

<h1>Using JavaScript</h1>

<!-- <![CDATA[

var quantity;

quantity = prompt("Type a quantity greater than 0");

if (quantity <= 0)

{

document.write("<p>Quantity is not greater than 0.</p>");

document.write("<p>Please refresh the web page.</p>");

} else {

document.write("<p>Quantity is greater than 0.</p>");

}

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