Date post: | 18-Jul-2015 |
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Introduction to JavaScript At First, Scripting Language developed by Sun Micro
Systems & Netscape jointly JavaScript was designed to add interactivity to HTML
pages JavaScript is a scripting language A scripting language is a lightweight programming
language JavaScript is usually embedded directly into HTML
pages JavaScript is an interpreted language (means that scripts
execute without preliminary compilation)
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Importance / facts Embedded into HTML Browser Dependent Interpreted Language Loosely Typed Language Object-Based Language Event-Driven Java Script is not java
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Importance ……… JavaScript is multifunctional i) Enhance HTML Pages ii) Develop client side applications iii) creates extensions to a webserver iv) Provide database connectivity without
using CGI
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Web Application FrameworkContent
Creation
Graphics Editor
HTML Editor
Browsers Client Extensions
Active X
Applets
Script ing
JavaScript
VB Script
Servers Server Extensions
Java script
Database ExtensionsODBC, JDBC
Security
Content Management
Search tools
Database Services
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JavaScript & HTML
JavaScript is integrated into HTML with <script> and </script> tags. Ex: <script language = “JavaScript”> </script>
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First program Ex: <script language=“JavaScript”> { Document.write(“Hello to script”); } </script>
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Ex program <HTML> <HEAD> <TITLE> JAVASCRIPT PROGRAM TESTING</TITLE> <SCRIPT LANGUAGE="JavaScript"> alert("Hello! everybody"); </script> </head> <body> testing script </body> </html>
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User Interaction <HTML> <HEAD><TITLE> Dialog Box from a function</TITLE> <SCRIPT LANGUAGE="JavaScript"> function opendoc() { alert(“dialog called from function"); } </script></head> <body><b>Push button test</b> <FORM METHOD=“POST”> <INPUT TYPE=Button Name=“B1” VALUE=“push”
onClick=“opendoc()”></FORM> </body> </html>
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Identifiers, Keywords Variables or methods or objects Key words: break, if, this, continue, in, time, else,
but, false, new, while, for, null, with, function and return.
Literals: Integer, Floating, Boolean, String,
Special characters.
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Variables Variables are used to store the data. Ex: Var variablename; Types: Number, Boolean, String,
Function, Object A variable declared inside a function
has local scope.
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Global Scope Global variables are accessible to all
parts of an application including functions.
Global variable is created by initializing it directly and not using the keyword var.
Comments: // or /* ------*/
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Functions Declaration: function displaymessage() { document.write(“functions demo”); } A function is declared in the head part of
html.
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Looping for : for (initializing exp; condition-exp; loop-exp) { Statements; } Ex: for(var i=0;i<10;i++) { document.writeln(i); }
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for … in for .. in loop works with arrays. Ex: for (index in arrayName) { // some code } index is a variable that we declare prior to
loop, that will automatically populated with the next index value in array.
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Example: var myArray= new Array(“rama”, “ravana”); var elementIndex; for(elementIndex in myArray) { document. Write(myArray[elementIndex]); }
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While Loop While loop allows to test a condition and
keep on looping while it’s true. While loop is more useful when you don’t
know how many you will need to loop.
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do-while, break and continue break terminates the loop altogether continue skips the remaining statements
for the current loop,
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Object Model Java script is an object based
language. It has no inheritance. The relation between objects is not of
ancestor descendent but of container. When an objects properties or methods
are referenced is used to denoted ownership.
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Java Script Objects & Corresponding HTML tags
Window --- Frame <frame> History ---- Location ---- Document <BODY> form <FORM> Button <Input type = “button”> Checkbox < Input type = “checkbox” >
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Object Model HierarchyWindow
history location
text
Text area
form
frameDocument
password
hidden
checkbox
Select
link
Reset
submit
button
anchor image
radio
Navigator
String
Array
Date
Math
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Window object Browser runs in a window. This is highest level object. It contains all other navigator object. Two primary methods: open() – name of html page, internal name of
window, host features of the window – menu bar, tool bar, location, directories, document and status.
These are properties of window object.
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Ex: function a() { var k= window.open(“xyz.html”,
“mywin”,”menubar=yes, toolbar=yes, location=yes directories=yes, status=yes”);
}
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Properties with objects window.status = “this is displayed on
the status bar” HISTORY object To navigate to back page Window.history.back() Window.history.forward()
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Ex: Ex: function evalProtocol { if(curProtocol == “http:”) { alert(“from web”); else if(curProtocol == “file:”) alert(“from file”); else alert(“else where”); } }
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Location object properties Href: complete URL Protocol: initial element of a URL Hostname: Host and domain name or
IP address Host : Hostname: Port element of a
URL Port: communications port of server Pathname: path element of URL
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Continue…. Serach: query definition portion of URL Hash : Anchor name of url (begin with #) Opening a new URL: Window.location=http://www.snist.com/ Window.location.href = “href://
www.snist.com/”
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Document object This is important and is responsible for all the
actual content displayed on a given page. We can display dynamic HTML pages & all user
interface elements. Write() or writeln() method is used to display
content on page. This is equivalent of HTML document. It is a container for all HTML related objects
associated with <head><body> tags.
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Document continue….. <BODY [BACKGROUND = “backgroundImage”] [BGCOLOR = “backgroundColor”] [TEXT = “foregroundColor”] [LINK = “unfollowedLinkColor”] [ALINK = “activatedLinkColor”] [VLINK = “followedLinkColor”] [onload = “methodName”] [onUnload = “methodName”]>
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Form Object This allows users interactions. Gives life to static web pages. Properties: <FORM [NAME=“formName”] [ACTION=“ServerURL”] [ENCTYPE=“encodingType”] [METHOD = “GET|POST”] [TARGET = “windowName”] [onSubmit = “methodName”] </FORM>
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Text Object
Common element to gather data entered by user. <INPUT type=“text” [Name = “objectname”] [Value=“value”] [Size=size] [MAX.LENGTH = size] [onBlur = “methodname”] [onChange = “methodname”] [onFocus = “methodname”] [onSelect = “methodname”]
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Text Area Object < TEXTAREA [Name = “objectName”] [ROWS=“numRows”] [COLS=“numCols” [WRAP=“off | virtual | physical”] [onBlur = “methodname”] [onChange = “methodname”] [onFocus = “methodname”] [onSelect = “methodname”] </TEXTAREA>
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Password object <INPUT type=“password” [Name = “objectname”] [Value=“defaultpassword”] [Size=integer] Anchor Object: <A [HREF = URL ] Name = “objectname” [TARGET = “windowName”]>
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Button This is a generic object that we have to
add code for it to be useful. Submit button is used to submit form data. Reset button is for reset the values of all
controls of a form.
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Button properties<INPUT TYPE=“button | submit | reset”[NAME = “objectName”][VALUE=“labelText”][onClick = “methodName”]
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Select Object <SELECT> [Name = “objectname”] [Size=“numberVisible”] [MULTIPLE] [onBlur = “methodname”] [onChange = “methodname”] [onFocus = “methodname”] <OPTION VALUE = “optionValue”
<[SELECTED]>
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Radio Object <input> TYPE = “radio” [NAME = “groupName”] [VALUE = “value”][CHECKED] [onClick=“methodName”]> [displayText]
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Methods….. Length CharAt(pos) IndexOf (search text[startPos],[endpos]) Substring(startPos,endPos) Big Blink Fixed Fontcolor Fontsize Small Strike Sub Sup toLowerCase toUPperCase
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Date getDate() getDay() getHours() getMinutes() getMonth() getSeconds() getTime() getYear() getTimeZoneOffset() --- GMT etc..
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Set Methods of Date object setdate(value) setHours(value) setMinutes(value) setMonth(value) setSeconds(value) setTime(value) setYear(value)
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examples var today = newDate() Result = today.getDate() Other formats: getFullyear() returns a year in the yyyy
format getActualMonth() returns the actual
numeric value for the month getCalenderMonth() returns the name of
the month
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Date methods continue….. getActualDay() returns the actual numeric
value of the day of the week getCalenderDay() returns the name of the
day of the week
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Mathematical constants
Property Description
E Returns Euler's number (approx. 2.718)
LN2 Returns the natural logarithm of 2 (approx. 0.693)
LN10 Returns the natural logarithm of 10 (approx. 2.302)
LOG2E Returns the base-2 logarithm of E (approx. 1.442)
LOG10E Returns the base-10 logarithm of E (approx. 0.434)
PI Returns PI (approx. 3.14)
SQRT1_2 Returns the square root of 1/2 (approx. 0.707)
SQRT2 Returns the square root of 2 (approx. 1.414)
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Math Object abs(value) absolute value acos(value) arc cosine value in radians asin(value) arc sine of value in radians atan(value) arc tangent of value in radians ceil(value) Cos(value) cosine value floor(value)
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Math continue exp(value) Euler’s constant to the power of value
(euler’s constant: 2.718) log(value) max(value) min(value) pow(value) round(value) sin(value) sqrt(value) tan(value)
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Arrays <html> <body>
<script type="text/javascript"> var i; var mycars = new Array(); mycars[0] = "Saab"; mycars[1] = "Volvo"; mycars[2] = "BMW";
for (i=0;i<mycars.length;i++) { document.write(mycars[i] + "<br />"); } </script> </body> </html>
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Join two arrays <html> <body>
<p id="demo">Click the button to join three arrays.</p>
<button onclick="myFunction()">Try it</button>
<script type="text/javascript"> function myFunction() { var hege = ["Cecilie", "Lone"]; var stale = ["Emil", "Tobias", "Linus"]; var kai = ["Robin"]; var children = hege.concat(stale,kai); var x=document.getElementById("demo"); x.innerHTML=children; } </script> </body> </html>
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Remove the last element <!DOCTYPE html> <html> <body>
<p id="demo">Click the button to remove the last array element.</p>
<button onclick="myFunction()">Try it</button>
<script type="text/javascript"> var fruits = ["Banana", "Orange", "Apple", "Mango"]; function myFunction() { fruits.pop(); var x=document.getElementById("demo"); x.innerHTML=fruits; } </script> </body> </html>
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Creating custom objects
function object (parameter1, parameter2,…) { this.property1=parameter1 this.property2=parameter2 this.method1=function1 this.method2=function2 }
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Instantiating objects new operator is used for instantiating objects objectInstance= objectType(parameter1,
2,3,……) Ex: creating a book object using the
following code dbBook=new book(“beginning javascript”,
“paul wilton”, “Rs.400”, “ 1000”);
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Exception Handling The try...catch statement allows you to test a
block of code for errors. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs.
try { //Run some code here }catch(err) { //Handle errors here }
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The Throw Statement
The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages.
Syntax: throw exception
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Example
The example below determines the value of a variable called x. If the value of x is higher than 10, lower than 5, or not a number, then throw an error. The error is then caught by the catch argument and the proper error message is displayed:
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JavaScript facts JavaScript is Case Sensitive A function named "myfunction" is not the same as
"myFunction" and a variable named "myVar" is not the same as "myvar".
JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables, objects and functions.
White Space: JavaScript ignores extra spaces. You can add white
space to your script to make it more readable. The following lines are equivalent:
var name="Hege";var name = "Hege";