Post on 20-Dec-2015
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Browser ScriptingBrowser Scripting
JavaScript
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Dynamic HTMLDynamic HTML
XHTMLXHTML
content
CSSCSS
style rules
appearance
ScriptingScriptingLanguageLanguage
manipulatemanipulate
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IntroductionIntroduction
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Client-Server ArchitectureClient-Server Architecture
• In a client-server architecture, computations are done either in the client or in the server (or both)
• In some cases, we can choose whether to perform the computation in the client or the server side- For example, validating forms
• There are cases where we cannot choose where to perform the computation- For example, accessing a database
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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
• Flash- Developed by Macromedia (acquired by Adobe in 2005)
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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
• Interacting with the server (w/o browser refresh)
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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 4, and it is equivalent to JavaScript 2.0
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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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Dynamic HTML Content: Dynamic HTML Content: Example 2Example 2
<html>
<head><title>JS Example</title></head><body>
<h2>Before the script</h2><h1>
<script type="text/javascript">
document.write(new Date().toLocaleString())
</script>
</h1><h2>After the script</h2>
</body></html>
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Dynamic HTML Content: Dynamic HTML Content: Example 3Example 3
<h2>Hello and
<i><script type="text/javascript">
var 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-while
while (condition) {statements}
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VariablesVariables
• 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;- Without var, a variable is considered global
• A variable name consists of letters, digits, and underscores (_), - Does not begin with a digit
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Data TypesData Types
• Values have one of 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
- function (discussed later)
- 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
<script type="text/javascript">
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 constructs with the operator ()
• Syntax: function fname(args...) {statements}
• Usually, functions are defined at the head - Guarantees that functions are declared before used
• 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
• Parameters are passed to (and return from) functions by value- Assignment does not change the original parameter
• Objects are not copied but rather act as pointers- That is, properties of an object can be changed when
given as an argument of a function
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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- The ith argument is 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 includes 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) – converts the beginning of string 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
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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
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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
• 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]
• Out-of-bounds assignments automatically enlarge the array - 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 XHTMLJavaScript and XHTML
• 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 An Example - Format VerificationVerification
• 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()