Javascript

Introduction to Scripting
• Scripting Languages are mainly used to build the programming environment in
HTML document .It Makes Web pages dynamic and interactive.
• There are 2 types of scripting languages
• Client side scripting languages
• Are scripts that execute on client side or the browser. Browser Includes
Scripting Interpreter
• Eg: VBScript, JavaScript, Jscript and ECMA Script
• Server side scripting languages
• Are scripts that execute on server side
• Eg: PHP,JSP, ASP .NET

Features of JavaScript
 C-based language developed by Netscape
 Mainly used for client side scripting because it is supported by all
the browsers.
 Platform Independence
 JavaScript is NOT supported by old browsers (IE 1.0). You can
enable or disable JS in new browsers

How to start programming in JavaScript
• All JavaScript Code must be in between the below tags
<script>
// JavaScript Code goes here
</script>

How to start programming in JavaScript
• JavaScript can be embedded to any HTML code in two ways
–Immediate scripting
–Deferred Scripting

Immediate Mode Scripting
• SCRIPT tag can be placed in HEAD or BODY tag
• Placing JavaScript in the HEAD tag ensures readability.
• Scripts gets executed as the page loads.
<body>
<h4> Immediate Demo</h4>
<script language="JavaScript">
document.write("<h5> Using JavaScript</h5>");
</script>
</body>

JavaScript – lexical structure
• JavaScript is object based and action-oriented.
• JavaScript is case sensitive.
• A semicolon ends a JavaScript statement

Commenting
C
// comment single line
/* comment
multiple lines */
JavaScript
//comment single line
/* Comment
multiple Lines*/

Declaring a variable
C
//Declaring a variable
Int a=10;
Char c=‘a’;
Float f=1.12;
JavaScript
//No need of prior Declarations
Var a=10; //local
b=15; //global

Variables in Detail
• Must start with a letter or an underscore and can have digits.
• The Data type is automatically decided by the usage.
• Scope is by default global. If a variable is prefixed by the keyword ‚var‛
within a function then it is a local variable.
• The formal parameters are local to the function.
function demo()
{
var inum1 = 10; // Local to the function
inum2 = 20; // Global to the document.
}
demo(); // Invoking function
inum1 = inum1+1; // Error because inum1 is local variable
inum2 = inum2+1; // no Error

JavaScript – Implicit data types
• JavaScript recognizes the following implicit data types
– Number
– String
– Logical
– Object
– The special value null
• Type conversion
– JavaScript automatically converts between data types
str = ‚100‛, num1 = 10, num2 = 20
num3 = num1+ num2
strsum = str + num2
strsum = num2 + str
30
10020
20100

Output
C
Int a=10,b=25;
Printf(‚%d %d‛,a,b);
JavaScript
Var a=10; var b=25;
Document.write(a,b);

Control Structures
C
Conditional Control Structures
• If
• If else
• Switch
Loops
• For
• While
• Do while
JavaScript
‚Exactly the same as on left side‛

Functions
C
Int findSum(int a,int b)
{
Int c;
c=a+b;
Return c
}
findSum(10,15);
JavaScript
function findSum(a,b)
{
c=a+b;
Return c;
}
findSum(10,15);

Operators
C
Arithmetic Operators
+, ++, -, --, *, /, %
Relational Operators
==, !=, ===, !==, >, >=, < , <=
Logical Operators
&&, ||, !
Assignment Operators
=, +=, -=, *=, /=, %=
Strict equal (===)
Strict not equal (!==)
Returns true if the operands are not
equal and/or not of the same type.
JavaScript
‚Exactly the same as on left side‛

Dialog boxes (Window Object methods)
• Alert dialog box - alert(message)
– Takes in a string argument and displays an alert box.
• Prompt dialog box - prompt(message,[inputDefault])
– Displays a message and a data entry field
• Confirm dialog box - confirm(message )
– Serves as a technique for confirming user actions

Questions?
‚A good question deserve a good grade…‛

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Javascript

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