1 Browser Scripting JavaScript

2 Introduction

3 Client-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 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

5 About Applets An applet is a Java class that runs in a frame that is embedded in a Web page 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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7 Browser Scripting Browser scripts are procedural programs embedded inside HTML script Can read and manipulate HTML elements, CSS properties, and the browser itself

Web browser HTML Page: …code..… Internet HTML/HTTP TCP/IP HTML/HTTP TCP/IP Web (HTTP) Server HTML pages with embedded script built-in Script interpreter Web Architecture for Scripts ClientServer

9 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

10 JavaScript History Introduced in Netscape 2 (1996) Standardized by ECMA under the name ECMAScript ( ) The latest version is ECMAScript 3, and it is equivalent to JavaScript 1.5

11 JavaScript Basics

12 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

13 Dynamic HTML Content: Example 1 JS Example Before the script document.write(' In the script ') After the script

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15 Dynamic HTML Content: Example 2 JS Example Before the script document.write(new Date().toLocaleString()) After the script

16 Dynamic HTML Content: Example 3 Hello and hours = new Date().getHours(); if (hours < 10) { document.write("good morning") } else {document.write("good day") }.

17 Basic Constructs Statement blocks -Semicolon ( ; ) is optional at end of line var x=5 document.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}

18 Variables 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

19 Data 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...

20 Some of the Reserved Words abstract as break case catch class const continue default delete do in instanceof interface is namespace new null package private public return else export extends false final finally for function if implements import static super switch this throw true try typeof use var void while with

21 Operators Arithmetic: * / % Comparison: == != === !== > >= < <= Logical: & && | || ! Bitwise: & | ^ ~ > >>> String: + Assignments: = += -= *= /= <<= |=...

22 Types 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" ?

23 An Example for (var counter = 1 ; counter <= 8 ; ++counter) { var fontsize = counter + 10; fontsize+="pt"; document.write(" " + "Font size " + fontsize + " "); }

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25 Functions

26 Functions 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

27 Function Example function add(x,y) { return x+y; } sum = add(4,5); document.write("4+5="+sum);

28 Function 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

29 Undeclared 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

30 An 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");

31 Predefined 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 )

32 Variable 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...

33 Objects and Arrays

34 Object 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

35 Creating 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";

36 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")

37 Defining Methods Methods are associated with objects just like attributes function niceString() { return " " + this.make + " "+ this.year + " " } theNissan = {make:"Nissan",year:2003,color:"blue",str:niceString}

38 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;

39 Accessing 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)

40 The Complete Example function niceString() { return " " + this.make + " "+ this.year + " " } 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());

41 Array 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

42 Creating 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

43 Array 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]]

44 Miscellaneous

45 JavaScript and XHTML Strict Embedding JavaScript code inside XHTML may violate XML rules -e.g., x 2 One solution is to import JavaScript code from external files, e.g.: -Always a good habit... Another solution: wrap the code in an XML CDATA section

46 Wrapping Code in CDATA //<![CDATA[ regular JavaScript code... //]]>

47 The 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()

48 String 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)

49 An 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 }

50 The Math 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

51 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 of the default object var a, x, y var r=10 with (Math) { a = PI * r * r; x = r * cos(PI); y = r * sin(PI/2) }

52 The 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()