Page 190 - DCAP408_WEB_PROGRAMMING

Web Programming

Notes All right, what is JavaScript? Designed by Netscape Communications and Sun, it is a
“lightweight programming language that you can use to add dynamic effects to your Web
pages.” HTML has limitations, because it can only describe the way a page’s elements such
as text, forms, hyperlinks and tables look like; it cannot dictate how they behave which is
where JavaScript steps in. “The ability to embed JavaScript scripts in a Web page gives
you, the programmer, much more control over how your Web page behaves.” When you
use it in combination with the browser’s Document Object Model (DOM), JavaScript can
produce intricate, dynamic HTML effects as well as animation and sound.
If your job is in IS security, you must remember that JavaScript has a history of security
problems. Most of these security holes have been caught and fixed, “but new ones are
being discovered all the time.” So, a developer has to “keep up-to-date on the current
status” of patches and bugs.
The book’s lingo is simple. Try this: “The most important thing to know about using
functions is how to make them work. Only three conditions need to be met for a function
call to succeed. First, the function must have been previously defined in the program.
Second, the correct number of parameters must be passed to it. Lastly, the correct object
must be present - you cannot call the string object’s split function without a string object.”
A book to invoke before you launch upon your own project.

6.4 Summary

 JavaScript enabled browsers recognizes and uses the Document Object Model (DOM)
which makes them capable of recognizing individual objects in an HTML page after the
page has been rendered in the browser.
 Style Sheets are a language used for specifying formatting and layout properties for a document.

 When JavaScript Assisted Style Sheets (JSSS) are embedded in an HTML page, the JavaScript
DOM picks up a whole new set of objects which add to the standard DOM objects which
enables web developers to access every element of a web page whether this element
appears on the page when it is rendered in a client browser or not.
 Since JavaScript understands the DOM and can extend the DOM with the use of JSS in a web
page JavaScript understands objects such as text box which is an object belonging to the DOM.
 All objects have properties that determine the functionality of the object, methods which
allow access to these properties and events to appropriate JavaScript event handlers.

 To handle document objects JavaScript enabled browser creates an array in memory per
HTML object thus registering each of the objects.

 JavaScript provides access to the arrays and their elements. Using the Methods of the
object, specific object properties can be set too.
 Updating of any web page element based on client input to make the web page interactive
can be done by referencing the appropriate element in its associated array, which provides
access to each element of the web page.

 JavaScript provides ‘Event Handlers’ which facilitate the passing of knowledge to the
JavaScript that an ‘event’ has occurred.
 JavaScript event handlers can be divided into two types interactive and non-interactive.
JavaScript identifies a web page object first and chooses an appropriate event associated
with the object and JavaScript event handlers mapped to an objects event connect the
object event and JavaScript code snippets.

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