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Java. Script - a Brief Introduction Anupriya
What is Java. Script • Object based (not object oriented) programming language – very limited object creation – a set of pre-defined objects associated with • HTML document structure – many HTML tags constitute JS Objects • Browser functionality – provides a limited API to Browser functionality
Where did it come from • Originally called Live. Script at Netscape – started out to be a server side scripting language for providing database connectivity and dynamic HTML generation on Netscape Web Servers – Netscape decided it would be a good thing for their browsers and servers to speak the same language so it got included in Navigator – Netscape in alliance w/Sun jointly announced the language and its new name Java Script – Because of rapid acceptance by the web community Microsoft forced to include in IE Browser
Browser compatibility • For the most part Java Script runs the same way in all popular browsers • There are many areas where there are slight differences in how Java Script will run • there will be a separate set of slides addressing these differences.
Java. Script…Java ? • There is no relationship other than the fact that Java and Java. Script resemble each other (and C++) syntactically • Java. Script is pretty much the de-facto standard for client-side scripting (Internet Explorer also provides VBScript & JScript) • In Netscape browsers there is an API that allows Java. Script and Java applets embedded in the same page to converse
What can it be used for • Some pretty amazing things…. – Text animation – graphic animation – simple browser based application – HTML forms submission – client-side forms data validation (relieving the server of this task) – web site navigation
What do I need to get started • A web browser – Netscape Navigator 4. x or later – MS Internet Explorer 3. x or later • A text Editor – Wordpad/Notepad – Vi, Emacs
Putting Java. Script into your HTML • in an external file – collect commonly used functions together into external function libraries on the server • added benefit of privacy from curious users • in-line with your HTML • as an expression for an HTML tag attribute • within some HTML tags as Event Handlers
• • The indicates the end of an embedded script. • the “language” attribute indicates the script processor to be used • the “src” attribute indicates the URL of a file on the server containing the script to be embedded
Scripts • Since scripts are placed in line with HTML older browsers will attempt to render them as text. • To preclude this hide them in side of an HTML comment. • for Java. Script comments use // or /* */
Object Hierarchy window history link anchor textarea password layer radio checkbox document form button reset submit location applet link image file. Upload select option area
Objects • window - the current browser window • window. history - the Netscape history list • window. document - the html document currently in the browser client area • window. location - the browser location field • window. toolbar - the browser toolbar • window. document. link - an array containing all of the links in the document • window. document. anchor - an array of all the anchor points in the document
Objects (more…) • • • Window. document. layer - a named document layer window. document. applet - a named java applet area window. document. image- a named image tag window. document. area - a named area window. document. form - a named form or the default form ect, ect
A few examples. . . • window. location = “http: //www. yahoo. com” – will take you to the specified URL (like a goto) • window. history. back() – back() is a method on history – will be like clicking the back button in Nav 3 – in Nav 4 will take you back to prev window • window. history. goto(1) – takes you back to first URL in history array
The Object Model • It is very important to understand the object model • each object has its own properties, some of which are read only some of which you can set directly by assignment (as location) • each object also has a set of behaviors called methods
Object Model Text Object = HTML text tag B l u r () default. Value form name Select() type focus() value handle. Event Red - gettable and settable
Object Event Handlers • Most objects respond to asynchronous, user generated events through predefined event handlers that handle the event and transfer control to a user written event handling function • Each object has particular events that they will respond to • the way you specify an event handler is by adding an additional attribute to the HTML tag that specifies the particular handler •
Events • • • • on. Abort on. Blur on. Change on. Click on. Error on. Focus on. Load on. Mouse. Out on. Mouse. Over on. Reset on. Select on. Submit on. Unload
on. Abort • Activated when a user aborts the loading of an image
on. Blur • Used with frame, select, textarea and window objects • invoked when an object loses the focus • use with select, text and textarea for data validation
on. Change • Used with select, text and textarea objects • use instead of on. Blur to validate only if a value has changed
on. Click • Used with button, checkbox, link, radio, reset, and submit objects.
on. Error • Used with image and window objects to invoke a handler if an error occurs while an image or window is loading. • Setting window. onerror = null will prevent users from seeing Java. Script generated errors
on. Focus • Used with frame, select, textarea and window objects. • Just the opposite of on. Blur; i. e. invoked when the object gets focus.
on. Load • Used with window, frame and image objects (use with
on. Mouse. Out and on. Mouse. Over • Used with area and link objects • user moves mouse off of an area or link
on. Reset • Used with form objects
on. Select • Used with text and textarea objects • run some Java. Script whenever a user selects a piece of text in a text or textarea object
on. Submit • Use with form objects to run a handler whenever a form has been submitted. • Useful to validate all fields prior to actual submission
on. Unload • Just like on. Load but the handler is run when the window/frame is exited
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