1 Browser Scripting JavaScript. 2 Introduction 3 Client-Server Architecture In a client-server...

1

Browser ScriptingBrowser Scripting

JavaScript

2

IntroductionIntroduction

3

Client-Server ArchitectureClient-Server Architecture

• In a client-server architecture, computation is done

either in the client or in the server

• There are cases where we can choose whether to

perform the computation in the client or in the server

- For example, validating forms

• There are cases where we cannot choose where to

perform the computation

- For example, accessing a database

4

Client Side TechnologiesClient Side Technologies

• JavaScript

- Developed by Netscape, standardized by ECMA

- Supported by all browsers (although not all support the standard)

• VBScript

- Developed by Microsoft

- Supported only by Microsoft Internet Explorer

- A light version of Microsoft Visual Basic

• Java Applets

- Developed by Sun

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About AppletsAbout Applets

• An applet is a Java class that runs in a frame that is

embedded in a Web page

<object type="application/x-java-applet"

classid="myApplet.class" width="x" height="y">

• When a browser loads the Web page, the applet byte-

code (.class file) is downloaded to the client box and

executed by the browser

• Commonly used for games, graphics, etc.

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Browser ScriptingBrowser Scripting

• Browser scripts are procedural programs

embedded inside HTML

<script type="text/javascript">script</script>

<script type="text/vbscript">script</script>

• Can read and manipulate HTML elements, CSS properties, and the browser itself

Web browser

HTML Page:

<SCRIPT>

…code..…

</SCRIPT>

InternetHTML/HTTP

TCP/IP

HTML/HTTP

TCP/IP

Web

(HTTP)

Server

HTML

pages with

embedded

script

built-in

Script

interpreter

Web Architecture for ScriptsWeb Architecture for Scripts

Client Server

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Why are Scripts Needed?Why are Scripts Needed?

• Generating HTML content dynamically

• Monitoring and responding to user events

• Validating forms before submission

• Manipulating HTTP cookies

• Interaction among the frames and windows of

the browser

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JavaScript HistoryJavaScript History

• Introduced in Netscape 2 (1996)

• Standardized by ECMA under the name

ECMAScript (1997-1999)

• The latest version is ECMAScript 3, and it is

equivalent to JavaScript 1.5

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JavaScript BasicsJavaScript Basics

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JavaScript is NOT Java!JavaScript is NOT Java!

• JavaScript is not compiled

• JavaScript is typically executed by Web

browsers and not as stand-alone applications

• JavaScript and Java have some similarity in

syntax

• The choice of the name is mainly for historical

reasons

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Dynamic HTML Content: Dynamic HTML Content: Example 1Example 1

<html>

<head><title>JS Example</title></head> <body>

<h2>Before the script</h2>

<script type="text/javascript">

document.write('<h1>In the script<\/h1>')

</script>

<h2>After the script</h2>

</body></html>

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<html>

<head><title>JS Example</title></head><body>

<h2>Before the script</h2><h1>


document.write(new Date().toLocaleString())

</script>

</h1><h2>After the script</h2>

</body></html>

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<h2>Hello and

<i><script type="text/javascript">

hours = new Date().getHours();

if (hours < 10) { document.write("good morning") }

else {document.write("good day") }

</script></i>.

</h2>

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Basic ConstructsBasic Constructs

• Statement blocks

- Semicolon (;) is optional at end of line

var x=5document.write(x);

var x=5, y=7;document.write(x+y);

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

• Conditions: if, if-else, ?:, switch

x= (y>0)? y:0

• Loops: for, while, do-whilewhile (condition) {statements}

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VariablesVariables

• JavaScript variables are not typed! (but values are)

- var x = 5; x="abcd";...

• Thus, the value of a variable is characterized by both

value and type

• Variables are declared with var keyword:

- var x; var y=5;

• A variable name consists of letters, digits, and

underscores (_), and does not begin with a digit

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Data TypesData Types

• Values have one the following types:

- number: 5, 2.3, 0xFF, 6.67e-11

- object: new Date()

• Arrays: [1,"ab ba",17.234]

• null

- string: "Hello World"

- boolean: true, false

- undefined: no value assigned...You can use typeof(x)

to get the type of x:number, string, object...

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Some of the Reserved WordsSome of the Reserved Words

abstractas

breakcasecatchclassconst

continuedefault delete

doin

instanceofinterface

isnamespace

newnull

packageprivate

publicreturnelse

export extends

falsefinal

finallyfor

function

ifimplements

import staticsuperswitch

thisthrowtruetry

typeofusevar

void whilewith

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OperatorsOperators

• Arithmetic: + ++ - -- * / %

• Comparison: == != === !== > >= < <=

• Logical: & && | || !

• Bitwise: & | ^ ~ << >> >>>

• String: +

• Assignments: = += -= *= /= <<= |= ...

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Types of EqualityTypes of Equality

• The equals == checks if both operands are equal

after performing type conversion

• The equals === checks if both operands are of

the same type and equal

• Example:

- Is 34 == "34" ? Is 34 == "3"+"4" ?

- Is 34 === "3"+"4" ? Is 34 !== "3"+"4" ?

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An ExampleAn Example


for (var counter = 1 ; counter <= 8 ; ++counter) {

var fontsize = counter + 10; fontsize+="pt";

document.write("<p style='font-size: "+fontsize+"'>" + "Font size " + fontsize + " <\/p>"); }

</script>

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FunctionsFunctions

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FunctionsFunctions

• JavaScript functions are special objects with operator ()

• Syntax: function fname(args...) {statements}

• Usually, functions are defined at the head of the file

- Why?

• Some functions are predefined

- For example, parseInt(string)

• Functions can return values

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Function ExampleFunction Example

<html> <head> <script type="text/javascript"> function add(x,y) { return x+y; } </script> </head>

<body> <h1> <script type="text/javascript"> sum = add(4,5); document.write("4+5="+sum); </script> </h1> </body></html>

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Function ValuesFunction Values

• Numbers and Booleans are passed to functions

by value

• Objects and strings are passed to functions by

reference

• Numbers and Boolean values are always

returned by value

• Objects and strings are returned by reference

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Undeclared ArgumentsUndeclared Arguments

• Function may receive arguments without declaring them

• Within a function, its arguments are held in the

arguments array

- can be accessed with arguments[i]

- The number of arguments is arguments.length

• Hence, it is possible to define functions that take any

number of arguments

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An ExampleAn Example

What is the result of the following code?function myConcat(separator) { var result=""; // iterate through arguments for (var i=1; i<arguments.length; i++) { result += arguments[i] + separator; } return result;}

con = myConcat(", ","red","orange","blue");

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Predefined FunctionsPredefined Functions

• JavaScript include several predefined functions

• For example,

- eval(code-string) – gets a string of JavaScript code,

evaluates it and executes it

• It allows dynamic code execution

- parseInt(string) – takes a string argument and

converts its beginning to an integer (or return NaN)

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Variable ScopesVariable Scopes

• JavaScript variables are recognized inside their

declaration scope

• Hence, global variables should be declared

outside the functions

• A variable declared in a function can also be

global, if var is omitted

- However, avoid this bad style...

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Objects and ArraysObjects and Arrays

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Object ModelObject Model

• JavaScript objects are similar to associative arrays

• That is, an object associates identifiers (e.g., firstName)

with values (attributes) (e.g., "John")

• Those values may be other objects (nested objects)

• Those values can also be functions (methods)

- e.g., function setPersonAge(age) {this.age = age}

• When o.f() is invoked, o can be referred to as this

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Creating ObjectsCreating Objects

• Objects can be created in several ways:

• Object initializers

• Object assignments

var theNissan = {make:"Nissan", year:2003, color:"blue"}

theMazda = { make:"Nissan" } theMazda.year = 2002;theMazda.color="black";

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Creating Objects (cont)Creating Objects (cont)

• Object Constructors

- define a constructor function

- create the new object using new

function car(make,year,color) { this.make = make this.year = year this.color = color}

theHonda = new car("Honda", 2001, "green")

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Defining MethodsDefining Methods

• Methods are associated with objects just like attributes

function niceString() { return "<span style='color:"+ this.color + "'>" + this.make + " "+ this.year + "<\/span>"}

theNissan = {make:"Nissan",year:2003,color:"blue",str:niceString}

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Defining Methods (cont)Defining Methods (cont)

function car(make,year,color) { this.make = make this.year = year this.color = color this.str = niceString}

theHonda = new car("Honda", 2001, "green")

theNissan = {make:"Nissan", year:2003, color:"blue"} theNissan.str = niceString;

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Accessing Object PropertiesAccessing Object Properties

• Object attributes can be accessed in several ways:

- object.attName

- object["attName"]

• Thus, object methods are invoked in Java/C++ style:

- object.method(arguments)

• Alternatively:

- object["method"](arguments)

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The Complete ExampleThe Complete Example

function niceString() { return "<span style='color:"+ this.color + "'>" + this.make + " "+ this.year + "<\/span>"}

function car(make,year,color) { this.make = make; this.year = year; this.color = color; this.str = niceString}

var theHonda = new car("Honda", 2001, "green");

document.write(theHonda.str());

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Array ObjectsArray Objects

• Arrays are supported as objects

• Attribute length

• Methods include:

concat, join, pop, push, reverse, sort, shift, ...

• Arrays can be passed to functions as arguments

• The array is passed by-reference

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Creating ArraysCreating Arrays

• var a = ["red", "blue", "green"]

- Allocates an array of 3 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

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Array ElementsArray Elements

• Array elements need not have the same type

- arr1 = ["hello", 1, true]

• Java-like access: arr[i]

• Array indices need not be contiguous

- arr1[10] = 66

• Multi-dimensional arrays are arrays of arrays

- var matrix = [ [0, 1, 1], [1, 1, 0], [0, 0, 0]]

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MiscellaneousMiscellaneous

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JavaScript and XHTML StrictJavaScript and XHTML Strict

• Embedding JavaScript code inside XHTML may violate

XML rules

- e.g., x<5 && x>2

• One solution is to import JavaScript code from external

files, e.g.: <script type="..." src="jsfile.js"/>

- Always a good habit...

• Another solution: wrap the code in an XML CDATA

section

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Wrapping Code in Wrapping Code in CDATACDATA

<script type="text/javascript"/>

//<![CDATA[

regular JavaScript code

...

//]]>

</script>

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The String ObjectThe String Object

• JavaScript has a built-in String object

- not the primitive string!

• Create a String object from a string primitive:- myString = new String("This is a string object")

• Extract the primitive string from a String object:- str = myString.valueOf()

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StringString Common Methods Common Methods

• 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()

• valueOf()

• match(regexp)

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An Example - Format VerificationAn Example - Format Verification

• What does the following function do?function getString() { var result = null; while(result==null) { var answer = prompt("Your first name:") if(answer!=null) { result = new String(answer); result = result.toLowerCase().match("^[a-z]+$"); } if(result==null) { alert("Don't mess with me!") } } return answer }

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The The MathMath Object Object

• The object Math is used for mathematical operations

- E.g., Math.pow(x,2)

• Other useful functions:

• abs(x)

• round(x)

• ceil(x)

• floor(x)

• cos(x)

• sin(x)

• tan(x)

• exp(x)

• pow(x, y)

• sqrt(x)

• log(x)

• max(x, y)

• min(x, y)

• Math Also includes constants such as: Math.E, Math.PI

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The The withwith Statement 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 of the default object

var a, x, yvar r=10with (Math) { a = PI * r * r; x = r * cos(PI); y = r * sin(PI/2) }

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The Date ObjectThe Date Object

• Create the current date: new Date()

• Create an arbitrary date: new Date(date-string)

• Common methods of Date:• getDate()

• getFullYear()

• getMonth()

• getDay

• getTime()

• getHours()

• getMinutes()

• getSeconds()

• getMilliseconds()

• toLocaleString()

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