Javascript DBI – Representation and Management of Data on the Internet.

Javascript

DBI – Representation and Management of Data on the Internet

Overview

• A "scripting" language for HTML pages• Embed code in HTML pages so they are

downloaded directly to browser• The browser interprets and executes the script (it

is not compiled)• Do not declare data types for variables (loose

typing)• Dynamic binding – object references checked at

runtime

Overview (cont.)

• Scripts can manipulate "browser objects:"– HTML form elements– Images– Frames– etc.

• For security – cannot write to disk (when run on a client)

It is not Java

• Java :– compilation required– can create “stand alone” application– much more complex

• more commands

• more built-in functions

• object-oriented

Web browser

HTML Page:

<SCRIPT>

…code..…

</SCRIPT>

Desktop access

InternetHTML/HTTP

TCP/IP

HTML/HTTP

TCP/IP

Web

(HTTP)

Server

HTML

pages w/

embedded

script

Remote host

built-in

JavaScript

interpreter

Web Architecture for JavaScript"CLIENT" "SERVER"

Example<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML><HEAD><TITLE>An Hello World Example</TITLE><SCRIPT LANGUAGE = "JavaScript">document.writeln("<H1>Can't you find a better example than Hello World?</H1>);</SCRIPT></HEAD>

<BODY>  </BODY></HTML>

Past and Present

• Built into Netscape Navigator since v2.0 (early 1996)

• Developed independently of Java• Proprietary, but submitted as standard and built

into Microsoft IE 3.0 and later• Standardized by ECMA (European Computer

Manufacture’s Association) into ECMAscript• EMCAscript joins JavaScript and Jscript to one

standard

http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM

Client and Server

• JavaScript can be used – On the client side– On the server

• More reliable on client than Java right now

• Useful for developing interactive interface

• Also useful for "gluing" Java applets together

CGI and other Server-side Architectures

• Strengths– allows access to server

files and databases

– makes no assumptions about client computer capabilities, puts little burden on it

– easier to manage and control on server

– more secure for client

• Weaknesses– puts most of processing

load on server– requires round-trip for

every submission, using valuable bandwidth

– cannot provide instantaneous response expected with GUI

– less secure for server

JavaScript Reserved Keywords

• break• case• continue• delete• do• else • false• for

• function• if• in• new• null• return• switch• this

• true• typeof• var• void• while• with

Non Used Reserved Words

• catch• class• const• debugger• default• enum• export

• extends• finally• import• super• try

Javascript Variables

• Untyped!

• Can be declared with var keyword:var foo;

• Can be created automatically by assigning a value:foo=1; blah="Hi Rakefet";

Variables Names

• A variable name can be any valid identifier• The identifier is a series of characters

– Consisting of letters, digits, underscores (_) and dollar signs ($)

– Does not begin with a digit– Does not contain any space

• JavaScript is case sensitive

Variables

• Using var to declare a variable results in a local variable (inside a function)

• If you do not use var – the variable is a global variable

Literals

• The typical bunch:– Numbers 17 123.45– Strings “Let it be”– Boolean: true false– Arrays: [1,“ab ba”,17.234]

Arrays can hold anything!

Operators

• Arithmetic, comparison, assignment, bit wise, Boolean (pretty much just like Java)

+ - * / % ++ --

== != > < >= <=

&& || ! & | << >>

+= -= *= /= %=

Conditional Operators

• equalsif (a == b) {…}

• not equalsif (a != b) {…}

• greater than or equal toif (a >= b) {...}

• less than or equal toif (a <= b) {...}

Boolean Operators

• andif (true && true) {…}

• orif (true || false) {…}

• notif (! false) {...}

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<HTML><HEAD><TITLE>Using Variables</TITLE><SCRIPT LANGUAGE = "JavaScript">

var firstNumber = 11, secondNumber = 23, sum;sum = firstNumber + secondNumber;document.write("<FONT COLOR = 'blue' SIZE = '6'>The sum of " + firstNumber + " and " + secondNumber + " is </FONT>");document.write(" <FONT COLOR = 'magenta' SIZE = '7'>" + sum + "</FONT>");

</SCRIPT></HEAD><BODY>  </BODY></HTML>

Control Structures

• Some just like Java:if if-else ?: switch

for while do-while

• And a few not like in Javafor (var in object)

with (object)

JavaScript’s Basic Constructs

• sequence (block)

• condition (selection)

• loop (iteration)

JavaScript Constructs

• sequence (block)– executes with no conditions– semicolons optional using one statement per line,

but not a bad thing to use all the time

var metushelahAge = 130; var yourAverageAgeyourAverageAge = metushelahAge - 98var myObject = new Object("initial value")more statements here..…..…..

JavaScript Constructs

• condition (selection)if (condition) {statements if true}else {statements if false}

if (metushelahAge < yourAverageAge) { document.write ("<body><h2>its true that

Metushelah is younger than most of you,") document.write ("<br>computers never lie!</h2>

</body>")}

JavaScript Constructs• loop (iteration)

– both for and while loops are available, e.g.while (init expression; condition; update expression){statements}

for (var i=0; i < inputAge.length; i++) {var oneChar = inputAge.substring (i, i+1)if (oneChar < "0" || oneChar > "9") {

alert("Please enter a valid number “+ oneChar + " is not valid.")

}}

<HTML><HEAD><TITLE>Loops Example</TITLE><SCRIPT LANGUAGE = "JavaScript">

for (var counter = 1 ; counter <= 7 ; ++counter) { document.write(“<P><FONT COLOR = 'magenta' SIZE = ‘ “ + counter + “ '> Now with font size " + counter + " </FONT></P> “);

}</SCRIPT></HEAD>

<BODY>  </BODY></HTML>

Javascript Functions

• The keyword function used to define a function (subroutine):

function add(x,y) {

return(x+y);

}

Function Input and Outout

• Numbers and Boolean values always passed to functions using call-by-value

• For objects, a call-by-reference is used to pass them to the functions

• Numbers and Boolean values are always returned by value

• Objects returned by reference


<HTML><HEAD><TITLE>Functions Example</TITLE><SCRIPT LANGUAGE = "JavaScript">function fibonacciValue() { var value = parseInt(document.fibonacciForm.number.value ); window.status = "Calculating Fibonacci number for " + value; document.fibonacciForm.result.value = fibonacci(value); window.status = "Done Calculating Fibonacci number";}

function fibonacci( n ) { if (n == 0 || n == 1) // base case return n; else return fibonacci( n - 1 ) + fibonacci( n - 2 );}</SCRIPT></HEAD>

<BODY>

<FORM NAME = "fibonacciForm">

<TABLE BORDER = "1" BGCOLOR = "blue">

<TR><TD BGCOLOR = "cyan">Enter a number</TD>

<TD><INPUT NAME = "number" TYPE = "text"></TD>

<TD><INPUT TYPE = "button" VALUE = "Calculate"

ONCLICK = "fibonacciValue()"</TR>

<TR><TD BGCOLOR = "cyan">Fibonacci Value</TD>

<TD><INPUT NAME = "result" TYPE = "text"></TD></TR>

</TABLE>

</FORM>

</BODY>

</HTML>

Global Functions (1)

• escape – changes characters in a string that are not in the ASCII characters set to HEX

• unescape – decodes the escape encoding

• eval – gets a string of JavaScript code, evaluates it and executes it– It allows dynamic code execution


• isNaN – takes a numeric argument and returns true if the value is not a number

• parseFloat – takes a string argument and converts its beginning to a float number (or return NaN)

• parseInt – takes a string argument and converts its beginning to an integer number (or return NaN)


• isFinite – given a numeric argument it returns true if the argument is not– NaN– Number.POSITIVE_INFINITY– Number.NEGATIVE_INFINITY

Objects

• Objects have attributes and methods

• Many pre-defined objects and object types

• Using objects follows the syntax of C++/Java:objectname.attributename

objectname.methodname()

Array Objects

• Arrays are supported as objects

• Attribute length

• Methods include:concat join pop push reverse sort

Creating a New Array

• var a = [“red”, “blue”, “green”, “yellow”]– Allocates an array of 4 cells and initializes the

values

• var b = new Array(5)– Allocates an array of 5 cells without initializing

values

• var c = new Array()– Creates a new empty array

Array Example Code

var a = [8,7,6,5];

for (i=0;i<a.length;i++)

a[i] += 2;

b = a.reverse();

Passing Arrays to Functions

• Arrays can be passed to functions as arguments

• The array is passed by call-by-reference

• The name of the array is given to the function

<HTML><HEAD><TITLE>Arrays Example</TITLE><SCRIPT LANGUAGE = "JavaScript">function start() { var colors = ["red", "blue", "green"] printArray(colors); printArray(colors); }

function printArray( colorsArray ) { // prints the array but also modifies it for (var i in colorsArray) {

var c = colorsArray[i];document.writeln("<FONT SIZE = 5 COLOR =" + c + "> " + c + " </FONT><BR>");colorsArray[i] = "gray";

}}</SCRIPT></HEAD><BODY ONLOAD = "start()"> </BODY></HTML>

Multidimentional Arrays

• var matrix = [ [0, 1, 1], [1, 1, 0], [0, 0, 0]];

• var myArray = [[1, 2, 3], [1], [1, 2]];

• Going over the array

for (var i in myArray ) {

for (var j in myArray[i])

document.write(myArray[i][j]);

Other Object Types

• String: manipulation methods• Math: trig, log, random numbers• Date: date conversions• RegExp: regular expressions• Number: limits, conversion to string

Math Common Methods

• abs(x)• round(x)• ceil(x)• floor(x)• max(x, y)• min(x, y)

• cos(x)• sin(x)• tan(x)• exp(x)• pow(x, y)• sqrt(x)• log(x)

Math Also includes constants

such as: Math.E, Math.PI

String Common Methods (1)

• charAt (index)• charCodeAt(index)• Concat(string)• fromCharCode(value1

, value2, …)• indexOf(substring,

index)• lastIndexOf(substring,

index)

• slice(start, end)• split(string)• substr(start, length)• substring(start, end)• toLowerCase()• toUpperCase()• toString()• valueOf()

Methods that Generate HTML• anchor(name) – wraps the source with

– <A name = name></A>• big() – wraps the source with

– <BIG></BIG>• blink() – wraps with

– <BLINK></BLINK>• bold() – wraps the source with

– <B></B>• fixed() – wraps the source with

– <TT></TT>

More Methods that Generate HTML

• fontcolor(color) – wraps with – <FONT color=“color”></FONT>

• fontsize(size) – wraps with – <FONT size=“size”></FONT>

• italic() – wraps with – <I></I>

• link(url)– <A href = url></A>

More Methods that Generate HTML

• small() – wraps the source with– <SMALL></SMALL>

• strike() – wraps the source with – <STRIKE></STRIKE>

• sub() – wraps the source with– <SUB></SUB>

• sup() – wraps the source with – <SUP></SUP>

Date Common Methods

• getDate(), getFullYear(), getMonth(), getDay

• getTime(), getHours(), getMinutes(), getSeconds(), getMilliseconds()

• All these have a version with UTC (e.g., getUTCDate()) for GMT (Greenwich Mean Time)

<HTML>

<HEAD><TITLE>Arrays Example</TITLE>

<SCRIPT LANGUAGE = "JavaScript">

function getTimes() {

var current = new Date();

var out = new String();

out = "Day: " + current.getDay()+"\n";

out = out.concat("Month: " + current.getMonth() + "\n");

out = out.concat("Year: " + current.getFullYear() + "\n");

out = out.concat("GMT Time: " + current.toUTCString() + "\n");

out = out.concat("Time: " + current.toString() + "\n");

timesForm.output.value = out;

}

</SCRIPT>

</HEAD>

Predefined Objects

• In JavaScript the following objects are automatically created for you (always available)– document– navigator– screen– window

The document Object

• Many attributes of the current document are available via the document object:

Title Referrer

URL Images

Forms Links

Colors

document write method

• document.write() like a print statement – the output goes into the HTML document

document.write("My title is" + document.title);

string concatenation

Objects Hierarchy

• JavaScript objects include object hierarchy + (property or method)– window.document.lastModified– metushelahBirthday.getYear()

• need not be fully qualified– document.lastModified

• proceeds from most to least general– window.document.forms[0].inputText1.value

• all names are case sensitive

Objects Object Oriented

• Objects – complex data types or “containers” that have both data and code

• Methods – code or “functions” that work on an object’s properties

• Properties – data that are stored and retrieved via object references

• This is not true "OO" because the object hierarchy is not extensible, you can create new objects, but cannot extend existing ones

The with Statement

• Establishes the default object for a set of statements

• Within the set of statements, any property references that do not specify an object are assumed to be for the default object

Example of with

var a, x, y

var r=10

with (Math) { a = PI * r * r x = r * cos(PI) y = r * sin(PI/2)

}

Dynamic HTML

HTML

CSSJava Script

HTML HTML

Dynamic HTML

What is Dynamic HTML

• Dynamic HTML (DHTML) is an all-in-one word for web pages that use – Hypertext Markup Language (HTML),

– Cascading Style Sheets (CSS), and

– rely on JavaScript to make the web pages interactive

• DHTML describes the abstract concept of – breaking up a page into manipulable elements

– exposing those elements to a scriping language

– the script perform the manipulations

Why Do We Need DHTML?

• HTML in its traditional form is not powerful enough to create the interactive and multimedia-rich documents

• Without DHTML, the browser must download another page from the server to change what the user sees on the screen

JavaScript (+)

• What JavaScript can do: – Control document appearance and content– Control the behavior of the browser– Interact with document content– Interact with the user– Read and write client state with cookies– Interact with applets– Manipulate embedded images

JavaScript(-)

• What JavaScript cannot do: – No graphics capabilities– No reading/writing of files on the client side– No networking except to arbitrary URLs– No multithreading

Dynamic HTML Object Model

• Gives access to all the elements on the Web page:– Frames

– Applets

– Images

– Forms

– StyleSheets

– etc.

• Scripts are used to dynamically change objects and thus the Web page

Document Object Model (D.O.M)

• When an HTML page loads into a scriptable browser, the browser creates a hidden, internal roadmap of all the elements it recognizes as scriptable objects

• The roadmap is hierarchical• The scriptable objects are “document objects”• Document objects in a page can be addressed and moved

around, font sizes and styles can change as the cursor travels over them … – all this is controlled by scripting

• Unfortunately, Netscape and Microsoft have somewhat incompatible implementations of DHTML

The Object Model

• Naming hierarchy used to access individual elements of a HTML document

• Easy to use if you name all entities:– Forms, fields, images, etc.

DOM Example<FORM NAME=myform ACTION=…Please Enter Your Age:<INPUT TYPE=TEXT NAME=age><BR>And your weight:<INPUT TYPE=TEXT NAME=weight><BR></FORM>

<FORM NAME=myform ACTION=…Please Enter Your Age:<INPUT TYPE=TEXT NAME=age><BR>And your weight:<INPUT TYPE=TEXT NAME=weight><BR></FORM>

• From JavaScript you can get the age input field as: • document.myform.age.value

Collections all and children

• all is used to refer to all the descendents of an object

• children is used to access only direct children

for(var loop=0; loop<document.all.length; ++loop)

elements += “<BR>”+document.all[loop].tagName;

Only in In Microsoft

Internet Explorer

Netscape vs. IE

• These features are specific to Netscape Navigator 4.0, and aren't supported by Microsoft: – <layer> tag– JavaScript Style Sheets– Bitstream fonts

IE vs. Netscape

• These features are specific to Microsoft Internet Explorer 4.0, and aren't supported by Netscape: – Direct Animation Controls– data binding– VBScript– OpenType fonts

The Solutions

• Use JavaScript to detect the browser– <SCRIPT LANGUAGE="JavaScript">– – </SCRIPT>

• The document.layers object is specific to Netscape 4.0, while the document.all object is specific to IE 4.0.

Some Important Objects• window:

– the top-level object – the window object is the "parent" object for all other objects in Navigator

– has properties that apply to the entire window – there is also a window object for each "child window" in a

frames document

• document: – contains properties based on the content of the document, such as

title, background color, links, and forms

• location: – has properties based on the current URL

• history: – contains properties representing URLs the client has previously

requested

window

plugins

document

document

document

frames

history

navigator

location

event

screen

all

collections

anchors

applets

body

embeds

images

forms

filters

links

plugins

styleSheets

scripts

objects In IE

In Netscape

Information about the Browser

• The Window object contains references to three objects that contain information about the browser or the browser window itself:– the Navigator object – the Location object – the History object

More System Info

function _get_version(){

return Math.round(parseFloat(navigator.appVersion) * 1000);}

function _get_os(){ if (navigator.appVersion.indexOf("Win95") > 0) return "WIN95"; else if (navigator.appVersion.indexOf("Win16") > 0) return "WIN31"; else if (navigator.appVersion.indexOf("Mac") > 0) return "MAC"; else if (navigator.appVersion.indexOf("X11") > 0) return "UNIX"; else return "UNKNOWN";}

Sys Info (cont.)

if (navigator.appName.substring(0,8) == "Netscape") {

// if so, set the name variable appropriately

browser.name = "NN";

// then parse navigator.appVersion to figure out what

// version

browser.version = _get_version();

// Then use appVersion again to determine the OS

browser.os = _get_os();

}

Sys Info (cont.)

else if (navigator.appName.substring(0,9) == "Microsoft") { browser.name = "MSIE"; browser.version = _get_version(); browser.os = "WIN95";}else { browser.name = navigator.appName; browser.version = _get_version(); browser.os = _get_os();}

Sys Info (cont.)

with (browser) {

document.write("<p>Name=", name);

document.write("<p>Version=", version);

document.write("<p>OS=", os);

}

<HTML>

<HEAD><TITLE>Arrays Example</TITLE>

<SCRIPT LANGUAGE = "JavaScript">

function start() {

window.alert( paragraphText.innerText );

paragraphText.style.color = 'red';

paragraphText.innerText = "Virus has been installed !!"

}

</SCRIPT>

</HEAD>

<BODY ONLOAD = "start()">

<FONT SIZE = '5'>

<P ID = "paragraphText">

A new virus is now being install in your computer.</P></FONT>

</BODY>

</HTML>

An Example

JavaScript Object Hierarchy

Window

Document

Form

parent

top

self

frames

link

anchorbutton

radio

checkbox

select

etc.

The window

• Next, we will examine what can be done with a window

• We follow Netscape properties and methods

Window Control

• Window.open(address)– Navigation– Status– Address

• Window.close(title)

Window Properties (1)

• closed Specifies whether a window has been closed • defaultStatus Reflects the default message

displayed in the window's status bar • document Contains information on the current

document, and provides methods for displaying HTML output to the user

• frames An array reflecting all the frames in a window

• history Contains information on the URLs that the client has visited within a window

http://developer.netscape.com/docs/manuals/communicator/jsref/win1.htm#1010680


http://developer.netscape.com/docs/manuals/communicator/jsref/doc1.htm#1048486



Windows Properties (2)

• innerHeight Specifies the vertical dimension, in pixels, of the window's content area

• innerWidth Specifies the horizontal dimension, in pixels, of the window's content area

• length The number of frames in the window

• location Contains information on the current URL

• locationbar Represents the browser window's location bar







• menubar Represents the browser window's menu bar

• name A unique name used to refer to this window • opener Specifies the window name of the calling

document when a window is opened using the open method

• outerHeight Specifies the vertical dimension, in pixels, of the window's outside boundary

• outerWidth Specifies the horizontal dimension, in pixels, of the window's outside boundary.







• pageXOffset Provides the current x-position, in pixels, of a window's viewed page

• pageYOffset Provides the current y-position, in pixels, of a window's viewed page

• parent A synonym for a window or frame whose frameset contains the current frame

• personalbar Represents the browser window's personal bar (also called the directories bar)





Window Properties (5)

• scrollbars Represents the browser window's scroll bars

• self A synonym for the current window• status Specifies a priority or transient message in the

window's status bar• statusbar Represents the browser window's status

bar• toolbar Represents the browser window's tool bar • top A synonym for the topmost browser window • window A synonym for the current window








Window Methods (1)

• alert Displays an Alert dialog box with a message and an OK button

• back Undoes the last history step in any frame within the top-level window

• blur Removes focus from the specified object • captureEvents Sets the window or document to

capture all events of the specified type • clearInterval Cancels a timeout that was set

with the setInterval method







Window Methods (2)

• clearInterval Cancels a timeout that was set with the setInterval method

• clearTimeout Cancels a timeout that was set with the setTimeout method

• close Closes the specified window • confirm Displays a Confirm dialog box with the

specified message and OK and Cancel buttons • disableExternalCapture Disables external

event capturing set by the enableExternalCapture method








Window Methods (3)

• enableExternalCapture Allows a window with frames to capture events in pages loaded from different locations (servers)

• find Finds the specified text string in the contents of the specified window

• focus Gives focus to the specified object • forward Loads the next URL in the history list • handleEvent Invokes the handler for the

specified event

Window Methods (3)

• home Points the browser to the URL specified in preferences as the user's home page

• moveBy Moves the window by the specified amounts

• moveTo Moves the top-left corner of the window to the specified screen coordinates

• open Opens a new web browser window

• print Prints the contents of the window or frame

Window Methods (4)

• prompt Displays a Prompt dialog box with a message and an input field

• releaseEvents Sets the window to release captured events of the specified type, sending the event to objects further along the event hierarchy

• resizeBy Resizes an entire window by moving the window's bottom-right corner by the specified amount

• resizeTo Resizes an entire window to the specified outer height and width

Window Methods (5)

• routeEvent Passes a captured event along the normal event hierarchy

• scroll Scrolls a window to a specified coordinate

• scrollBy Scrolls the viewing area of a window by the specified amount

• scrollTo Scrolls the viewing area of the window to the specified coordinates, such that the specified point becomes the top-left corner

Window Methods (6)

• setInterval Evaluates an expression or calls a function every time a specified number of milliseconds elapses

• setTimeout Evaluates an expression or calls a function once after a specified number of milliseconds has elapsed

• stop Stops the current download

The document

• Next, we will examine what can be done with a document

• We follow Netscape properties and methods

Properties of document

• alinkColor A string that specifies the ALINK attribute

• anchors An array containing an entry for each anchor in the document

• applets An array containing an entry for each applet in the document

• bgColor A string that specifies the BGCOLOR attribute

• cookie Specifies a cookie






Document properties (2)

• domain Specifies the domain name of the server that served a document

• embeds An array containing an entry for each plug-in in the document

• fgColor A string that specifies the TEXT attribute

• formName A separate property for each named form in the document






• forms An array a containing an entry for each form in the document

• images An array containing an entry for each image in the document

• lastModified A string that specifies the date the document was last modified

• layers Array containing an entry for each layer within the document

• linkColor (vlinkColor) A string that specifies the LINK (VLINK) attribute






• links An array containing an entry for each link in the document

• plugins An array containing an entry for each plug-in in the document

• referrer A string that specifies the URL of the calling document

• title A string that specifies the contents of the TITLE tag

• URL A string that specifies the complete URL of a document






Document methods (1)

• captureEvents Sets the document to capture all events of the specified type

• close Closes an output stream and forces data to display

• getSelection Returns a string containing the text of the current selection

• handleEvent Invokes the handler for the specified event

• open Opens a stream to collect the output of write or writeln methods






Document methods (2)

• releaseEvents Sets the window or document to release captured events of the specified type, sending the event to objects further along the event hierarchy.

• routeEvent Passes a captured event along the normal event hierarchy

• write Writes one or more HTML expressions to a document in the specified window

• writeln Writes one or more HTML expressions to a document in the specified window and follows them with a newline character





<HTML><HEAD><SCRIPT LANGUAGE="JavaScript1.1">// open a new windowvar n = window.open('', 'f',

'left=100,top=150,width=400,height=400');// dynamically create frames in that new window.// Note the use of about:blank URL to get empty framesn.document.write('<frameset rows="50%,50%"

cols="50%,50%">');n.document.write('<frame name="f1" src="about:blank">');n.document.write('<frame name="f2" src="about:blank">');n.document.write('<frame name="f3" src="about:blank">');n.document.write('<frame name="f4" src="about:blank">');n.document.write('</frameset>');

// An array of the colors we cycle through for the animation

colors = new Array("red","green","blue","yellow","white");

// An array of the frames we cycle through (in this order)

windows = new Array(n.f1, n.f2, n.f4, n.f3);

// The current color and frame counters

var c = 0, f = 0;

// A variable that holds the current timeout id (used to cancel the timeout)

var timeout = null;

function change_one_frame(){ // dynamically output the HTML necessary to set the

background color windows[f].document.write('<BODY BGCOLOR="' +

colors[c] + '">'); windows[f].document.close(); f = (f + 1) % 4; // increment frame counter c = (c + 1) % 5; // increment color counter // Arrange to be called again in 250 milliseconds // Save the timeout id so that we can stop this crazy thing. timeout = setTimeout("change_one_frame()", 250);}

</SCRIPT></HEAD><BODY onLoad="change_one_frame();"><FORM> <INPUT TYPE="button" VALUE="Stop" onClick="if (timeout) clearTimeout(timeout); if (!n.closed)

n.close();"></FORM></BODY></HTML>

Javascript Events

• JavaScript supports an event handling system– You can tell the browser to execute JavaScript

commands when some event occurs– Sometimes the resulting value of the command

determines the browser action

Events on TAGS

• If an event applies to an HTML tag, then you can define an event handler for it

• The name of an event handler is the name of the event, preceded by "on“

• For example, the event handler for the focus event is onFocus

• The general syntax is<TAG eventHandler="JavaScript Code">

Handling Events

• In Navigator 4.0, JavaScript includes event objects as well as event handlers

• Each event has an event object associated with it• The event object provides information about the

event, such as the type of event and the location of the cursor at the time of the event

• When an event occurs, and if an event handler has been written to handle the event, the event object is sent as an argument to the event handler

Handeling the Event

• Next, you need to define a function that handles the event

• The argument evnt is the event object for the event

function clickHandler(evnt) {

//What goes here depends on how you want to handle the event.

}

JavaScript Object Eventswindow, e.g. browser’s viewable area

document, e.g. home.html

text1 text2

text4text3

A B C D

1 2 3 4 5 6 7 8

Submit Button

Form #1, e.g. user-input

changing

the text

triggers

“onChange”

event

clicking

the button

triggers

“onClick”

event

Events Example

<BODY BGCOLOR=WHITE onUnload="restore()"><H5>Hello - I am a very small page!</H5><SCRIPT>savewidth = window.innerWidth;saveheight = window.innerHeight;function restore() { window.innerWidth=savewidth; window.innerHeight=saveheight;}// Change the window size to be smallwindow.innerWidth=300; window.innerHeight=50;document.bgColor='cyan';</SCRIPT>

Invocations

• Three types of invocation:– Immediate– Deferred– Hybrid

Immediate Invocation

<html><body>

<h1>Immediate invocation of JavaScript</h1>

<script language="JavaScript">



</script>

</body></html>

Deferred Invocation<html><head><script language="JavaScript">function showDate() {

document.write("<hr><p>This page was updated on " + document.lastModified + ".</p>")

} </script></head><body><h1>Deferred invocation of JavaScript</h1><form><input type="button" name="test" value="showDate"

onClick="showDate()"></form></body></html>

<HTML><HEAD><TITLE>Invocation Example</TITLE><SCRIPT LANGUAGE = "JavaScript">

document.writeln("<FONT SIZE = '5' COLOR = 'blue'>Script at the head of the Document</FONT>");

function p1() {

window.confirm("Continue?");document.writeln("<FONT SIZE = '5' COLOR = 'orange'>At function p1</FONT>");

}

function p2() {document.writeln("<FONT SIZE = '5' COLOR = 'orange'>At function p2</FONT>");

}</SCRIPT></HEAD> Invocations Example

<BODY ONLOAD = "p1()"><FONT SIZE = '5'> <P ID = "paragraphText">Some Text in the document body</P></FONT>

<SCRIPT LANGUAGE = "JavaScript">document.writeln("<FONT SIZE = '5' COLOR = 'orange'>At a script in the body</FONT>");

p2();</SCRIPT><P>After the script in the body.

</BODY></HTML>

Immediate Invocation

• In forms handling, unless the form is already populated, immediate does not make any sense

• An immediate invocation will run the JavaScript immediately!

Deferred Invocation

• onSubmit

• onClick

• onBlur

• onChange

• onFocus

• Located in the <Head>

Some More Events

• onCut, onCopy, onKeydown, onKeyPressed

• onDrag, onDrop, onDoubleClick, onMouseDown, onMouseUp, onDragOver, onDragEnter, onDragLeave

• onScroll, onResize, onSelect, onStop, onUnload

Dialog Boxes

• alert(“This is a JavaScript alert”)– user can “escape” to proceed

• confirm(“Are you sure you want to submit this?”)– user must respond yes or no

• var myAge = prompt(“Enter your age”)– user must enter an input string– resulting input is assigned to variable

Buttons

• You can associate buttons with JavaScript events (buttons in HTML forms)

<FORM>

<INPUT TYPE=BUTTON

VALUE="Don't Press Me"

onClick="alert('now you are in trouble!')“ >

</FORM>

<FORM>

<INPUT TYPE=BUTTON

VALUE="Don't Press Me"

onClick="alert('now you are in trouble!')“ >

</FORM>

Some Events (a small sample)

onUnLoad

onLoad

onClick

onMouseUp

onMouseDown

onDblClick

onMouseOver

Window events

Button events

Link events

onBlur v. onClick

• Checks one at a time• Can get tedious • Can get frustrating to

the user• Easier to write

• Checks on click• Bulk checking• Entire validation, all at

once• Harder to write

Form Validation

• You can have JavaScript code that makes sure the user enters valid information

• When the submit button is pressed the script checks the values of all necessary fields:– You can prevent the request from happening

Sample Deferred

Form Validation

<script language="JavaScript">

function validate(form) { var error = "";

if (form.text.value = = "") { error += "Please fill in the text.\n"; }

if (error != "") { alert(error); return (false); } else { return (true);}

</script>

Checking Fields

function checkform() { if (document.myform.age.value == "") { alert("You need to specify an age"); return(false); } else { return(true); }}

function checkform() { if (document.myform.age.value == "") { alert("You need to specify an age"); return(false); } else { return(true); }}

Needs to return true or false!

The Form<FORM METHOD=GET ACTION=foo.cgi

NAME=myform

onSubmit="return(checkform())">

AGE: <INPUT TYPE=TEXT NAME=Age>

<INPUT TYPE=SUBMIT>

</FORM>

Needed to prevent the

browser from submitting!

Important Note about Form Validation!!!

• It's a good idea to make sure the user fills out the form before submitting

• Users can bypass your form – they can create requests manually (or their own forms)

• Your CGI programs cannot rely (solely) on Client-Side JavaScript to validate form fields!

Setting Cookies

Function setCookie(name, value, expires) {

document.cookie = name + “=“ + escape(value) + “; path=/”+

((expires == null) ? “ “ ; expires=“ +

expires.toGMTString());

}

var exp = new Date ();

exp.setTime(exp.getTime() + (1000 * 60 * 60 * 24 * 31));

setCookie(“myname”, “myvalue”, exp);

Retrieving Cookiesfunction getCookie(name) {var cname = name + “=“;var dc = document.cookie;if (dc.length > 0) {

begin = dc.indexOf(cname);if (begin != -1) {

begin += cname.length;end = dc.indexOf(“;”, begin);

if (end == -1) end = dc.lengthreturn unescape(dc.substring(begin, end));

}}

return null;}

Moving Objects

• Next, we give an example of moving objects on the screen

<HTML><HEAD><TITLE>Moving Objects</TITLE></HEAD><BODY onLoad=“moveIt()><DIV ID="shape1" STYLE="position:absolute; left:100;

top:50; width:300; height:100; clip:rect(0,300,100,0); background-color:red; layer-background-color:red; z-index:2;">

</DIV><DIV ID="shape2" STYLE="position:absolute; left:150;

top:100; width:300; height:100; clip:rect(0,300,100,0); background-color:yellow; layer-background-color:yellow; z-index:1;">

</DIV></BODY></HTML>

function moveIt() {//Get the client window width and height on the initial load. if (firstTime) { if (document.all) { // Internet Explorer maxHeight = document.body.clientHeight-imageHeight maxWidth = document.body.clientWidth-imageWidth } else { // Netscape maxHeight = window.innerHeight-imageHeight maxWidth = window.innerWidth-imageWidth } firstTime = false chgXBy = 1 chgYBy = 1 }

//Get the current position of our image. if (document.all) { // Internet Explorer topPos = document.all.mover.style.pixelTop leftPos = document.all.mover.style.pixelLeft } else { // Netscape topPos = document.mover.top leftPos = document.mover.left }

//If any boundaries have been hit, change direction. //Upper Boundary if (topPos >= maxHeight) { chgYBy = -1 } //Right Boundary if (leftPos >= maxWidth) { chgXBy = -1 } //Lower Boundary if (topPos <= 0) { chgYBy = 1 } //Left Boundary if (leftPos <= 0) { chgXBy = 1 }

//Set the new position of the image. topPos += chgYBy leftPos += chgXBy

if (document.all) { // Internet Explorer document.all.mover.style.pixelTop = topPos document.all.mover.style.pixelLeft = leftPos } else { // Netscape document.mover.top = topPos document.mover.left = leftPos }//Iterate every 20 milliseconds setTimeout("moveIt()",20)}

Javascript DBI – Representation and Management of Data on the Internet.

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