Introduction to JavaScript

Dr. John P. Abraham

University of Texas – Pan American

What is JavaScript

• Object-based scripting language

• Developed by Sun Microsystems

• Syntax is similar to C++

• HTML is static, JavaScript adds interactivity.

• JavaScript can store information as cookies.

SCRIPTING LANGAUGES

• Programming languages developed to serve a particular purpose.

• JAVA SCRIPT was developed to add interactivity to Web pages

• Interpreted rather than compiled• Interpreter is built into the web browsers• First made available as part of Netscape 2.0

(Javascript created by Brendan Eich of Netscape)

Flavors of Java Script

• Core– Basic JavaScript language. It includes the

operators control structures and built-in functions.

• Client side

• Server side

Client side javascript

– Extends the core to provide access to browser and documents via DOM (document Object Model). Runs on the client’s (visitor) computer.

– Example an image on the web page can be manipulated by JavaScript, we can change its source property (src) to display a different image in response to something the user is doing such as moving the mouse.

– Javascript can be used to create cookies and read from it.

– Also can be used for form validation saving time for a response from the server.

Popular Uses for JavaScript

• Client must have javascript enabled browser• Rollovers, status bar messages, browser

detection, redirecting the visitor, random images and quotes, pop-up windows, form validations, loading multiple frames at once, cookies, slide shows, calculations, plug-in detection, random sounds, cycling banners, displaying current date, displaying last modified date, etc.

Server side (SSJS)

• Provides access to databases and converts results into HTML format and delivers to the browser.

Other approaches to making web interactive

• Common Gateway Interface, CGI• Java applets,• Client pull (eg <meta http-equiv=“refresh” content

= “7”> reload every 7 sec.• Server push. (server maintains the connection and

delivers additional data over a period of time)• Plug-ins (adds animation and interactivity)• Various other scripting languages

Web programming

• Web applications

• Many scripting languages available

• I assign these languages to different groups

• I begin with Java Scripting also introduce ASP.NET

• Most web applications work with a DBMS, mySQL, MSSQL, Oracle

• Database server can reside on another computer

Client/Server Application

• Server Computer (Web server, IIS, Apache)

• Client Computer (web browser, explorer, firefox)

• Requests are sent

• Responses are received

• Communication takes place using HTTP (Hypertext transfer protocol)

Web browser

• Runs at the client site• Provides an user interface for the application• What is displayed is a web page• Each web page is identified by a URL and

defined by a web form • Web form is designed using HTML• The request to a server is sent using Hypertext

transfer protocol (HTTP)• A web page does not change depending on the

request is known as a static page

Client/Server Interaction using HTTP (Static)

• Into a web browser the user types an URL or clicks on a link pointing to a URL

• The web browser uses HTTP to send the request to the web server. The request contains several pieces of information, address of the requester, address of the server including the page requested (URL). Etc.– URL contains protocol, domain name, path and file name

• When the server receives the request it retrieves the page and sends it as the HTTP response.

• The browser receives the information and formats it and displays it.

Default

• If a document name is omitted, it looks for default.htm, default.asp, index.htm, or iisstart.asp.

Client/Server Interaction using HTTP (Dynamic)

• A dynamic page does not exist on the disk at the server, it is a form that contains server controls such as labels, buttons, or text boxes.

• The page is dynamically generated at the server• The request sent to the server contains the URL and

information entered by the user• When the server receives the request it looks at the

extension (htm, html, aspx, cgi, etc). The first two are static. Others are handed over to the appropriate application server to assemble the page as an HTML document.

• The browser receives the information and formats it and displays it.

JavaScript and HTML

• HTML tag attributes can be accessed as object properties with javaScript.

• Document.bgcolor=“white”

• Document.write(“Hello”)

• You can even use script to write html– Document.write(“h1

align=center>Hello</h1>”)

Example of html with script

<html><head><title>Script 1.1: Using the Write Method</title></head><body bgcolor="white" text="black"><script language="JavaScript" type="text/javascript">

document.write("Hello")</script></body></html>

Run

Example 2

<html><head><title>Script 1.3: Changing Background &amp; Foreground

Colors</title></head><body bgcolor="white" text="black"><script language="JavaScript" type="text/javascript">

document.write("<h1 align=center>Hello</h1>")document.bgColor = "blue"document.fgColor = "white"

</script></body></html>

Script in HTML head

<script type = “text/javascript”> says it a text file and the scripting language is javaScript

<!— Those browsers that do not support script will consider this as comments and ignore

SCRIPT CODE HERE

//

Document Object

• The most import object in JavaScript is the document object

• To refer to a method for this object we write:

• document.write(“hello”)• document.write(“<h1 align=center>

hello”</h1>”)• document.bgColor = “blue”

Obtaining user input with prompt dialog

• After <script – declare variables

• Var visitorName

• Read it this way:– vistorName=window.prompt(“Please enter your

name”);

• Display it– Document.writeln(“Hello, “ + name)

Arithmatic

+ - * / %

Show the rolls program here

Examine properties

• Document.write (“appName: “, navigator.appName);– Microsoft explorer

• Document.write(“Window location: “,window.location)– File:///A:/script.html

• Document.write(“history: “, window.history.length)– Length: 1

The Event Model• Most popularly capture events

– Load – finishes loading a page– Unload – loads a new one– Mouseover – mouse moved– Mouseout – move mouse off of object– Click – Focus – make active an object– Change – changes data selected– Submit – submits a form– Reset – resets a form

• Event handlers are onLoad, onClick, onChange, etc.

• http://members.ozemail.com.au/~dcrombie/javascript/chap07.html

First JavaScript program

<html><head>

<title>Reporting Browser Information</title></head><body><h1>Your Browser</h1><script language = "JavaScript" type ="text/javascript">document.write("<b>appCodeName:</b> ", navigator.appCodeName, "<br>")document.write("<b>appName:</b> ", navigator.appName, "<br>")document.write("<b>appVerson:</b> ", navigator.appVersion, "<br>")document.write("<b>Platform:</b> ", navigator.platform, "<br>")</script></body></html>

JAVA SCRIPTHOW TO PROGRAM

DR. JOHN ABRAHAMPROFESSOR

UTPASOME SLIDES FROM W3SCHOOLS

SCRIPT IN BODY OF HTML

<html>

<body>

<script>

document.write("Hello World!");

</script>

</body>

</html>

FUNCTIONS IN THE HEADING

<html><head><script type="text/javascript">function message(){alert("This alert box was called with the onload event");}

</script></head>

<body onload="message()">

</body></html>SEE NEXT SLIDE FOR RUN

PROGRAM RUN

Scripts in the head section:

Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it. 

Scripts in the body section:

Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page.

Using an External JavaScript

Sometimes you might want to run the same JavaScript on several pages, without having to write the same script on every page.To simplify this, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension.

Explain future value program