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Source: Web Page Design Using JavaScript
THE BASICS
JAVASCRIPT uses a subset of the programming language JA VA to provide a high level
of interactivity on a web page. JavaScripts are stored within an HTML document and are
interpreted by the web browser.
JavaScripts may be located within the HTML code at the point in the page where they
are to appear on the screen or they may be written using functions. Functions are small
subprograms that are stored between the head tags of an HTML document and are called on to
be executed when a particular event occurs.
Whether the script is stored between the head tags or within the body of the HTML
document, it must be enclosed in script tags. Also, a set of HTML comment tags are typically
used inside the script tags so that older browsers that do not support JavaScript will ignore the
script and continue to process the page without errors.
Following is an example of the script and comment tags:
<script language="javascript">
<!--
Include JavaScript Code Here
.the difference between a working script and an error message can be one capital letter.
ALERT BOXES
To pop up an alert box include the following line of code inside of script tags in the body
of your HTML document. Please note that the processing of the page will stop until the
viewer responds to the alert box.
alert ("Place the text to be displayed in the alert box between these quotes.")
Other types of pre-made dialog boxes are available such as the prompt and confirm
boxes. In order to take full advantage of the features of these dialog boxes you must write
more JavaScript code which can use the values that are returned by the dialog boxes.
The following statements will pop up a dialog box that requires a yes or no answer (OK
or Cancel). If the answer is OK then the variable named answer has a value of true and if the
answer is Cancel then the variable named answer has a value of false. You can then use an if
statement in the JavaScript code to respond appropriately.
var answer = confirm ("Are you sure you want to quit?")
if (answer==true)
{
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