Javascript

INTRODUCTION JavaScript (aka ECMAScript) is an easy way to make your website visually attractive to clients and other viewers by adding interactivity and dynamics to HTML pages. Explains ABOUT: why one would use JavaScript in their HTML website design. It also has links to JavaScript tools, readings and samples for those who prefer ready-to-run effects.

What is java script JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Firefox Chrome, Opera, and Safari. JavaScript is a scripted language which is object oriented, event-driven, and platform independent. Each of these modern concepts in programming methodology are easier to work with in 'new' languages rather than being bolted on to older ones. And the syntax is similar to that of C and Java. This makes JavaScript a 'good' choice for learning as a first programming language.

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) Everyone can use JavaScript without purchasing a license

Why should a webpage author use JavaScript in addition to HTML?

Java script allows client-side user form validation Java script provides seamless integration with user plug-ins Java script allows access to some system information

Are Java and JavaScript the same? NO! Java and JavaScript are two completely different languages in both concept and design! Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.

The Real Name is ECMAScript: JavaScript's official name is ECMAScript. ECMAScript is developed and maintained by the ECMA organization. ECMA-262 is the official JavaScript standard. The language was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all Netscape and Microsoft browsers since 1996. The development of ECMA-262 started in 1996, and the first edition of was adopted by the ECMA General Assembly in June 1997. The standard was approved as an international ISO (ISO/IEC 16262) standard in 1998. The development of the standard is still in progress.

EXAMPLES Put a JavaScript into an HTML page <html><body><script type="text/javascript">document.write("Hello World!");</script></body></html> HELLO WORLD

JavaScript is Case Sensitive: Unlike HTML, JavaScript is case sensitive - therefore watch your capitalization closely when you write JavaScript statements, create or call variables, objects and functions. JavaScript Statements: A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do. This JavaScript statement tells the browser to write "Hello Dolly" to the web page: Note: Using semicolons makes it possible to write multiple statements on one line.

Java Script Comments Comments can be added to explain the JavaScript, or to make the code more readable. >Single line comments start with “//”:. >JavaScript Multi-Line Comments: Multi line comments start with /* and end with */. <script type="text/javascript">// Write a headingdocument.write("<h1>This is a heading</h1>");// Write two paragraphs:document.write("<p>This is a paragraph.</p>");document.write("<p>This is another paragraph.</p>");</script> THIS IS HEADING THIS IS HEADING THIS IS HEADING

Java variables JavaScript Variables As with algebra, JavaScript variables are used to hold values or expressions. A variable can have a short name, like x, or a more descriptive name, like car name. Rules for JavaScript variable names: Variable names are case sensitive (y and Y are two different variables) Variable names must begin with a letter or the underscore character Note:Because JavaScript is case-sensitive, variable names are case-sensitive.

Declaring (Creating) JavaScript Variables Creating variables in JavaScript is most often referred to as "declaring" variables.You can declare JavaScript variables with the var statement. EXAMPLE: var x;varcarname; Assigning Values to Undeclared JavaScript Variables: If you assign values to variables that have not yet been declared, the variables will automatically be declared. These statements: x=5;carname="Volvo";

Redeclaring JavaScript Variables As with algebra, you can do arithmetic operations with JavaScript variables: y=x-5;z=y+5; JavaScript Operators = is used to assign values. + is used to add values. JavaScript Arithmetic Operators Arithmetic operators are used to perform arithmetic between variables and/or values. Given that y=5, the table below explains the arithmetic operators: EXAMPLES: + , -, *, /, %

JavaScript Assignment Operators Assignment operators are used to assign values to JavaScript variables. Given that x=10 and y=5, the table below explains the assignment operators: OPERATORS =, += ,-=, *=, /=, %= The + Operator Used on Strings The + operator can also be used to add string variables or text values together. txt1="What a very";txt2="nice day";txt3=txt1+txt2;

Adding Strings and Numbers The rule is: If you add a number and a string, the result will be a string! x=5+5;document.write(x);x="5"+"5";document.write(x);x=5+"5";document.write(x);x="5"+5;document.write(x);

Logical Operators Logical Operators: Logical operators are used to determine the logic between variables or values. Given that x=6 and y=3, the table below explains the logical operators:

Conditional Operator Syntax Example: If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value "Dear President " else i t will be assigned "Dear".

Conditional Statements: Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this. In JavaScript we have the following conditional statements: if statement- use this statement to execute some code only if a specified condition is true if...else statement- use this statement to execute some code if the condition is true and another code if the condition is false if...else if....else statement- use this statement to select one of many blocks of code to be executed switch statement - use this statement to select one of many blocks of code to be executed

The JavaScript Switch Statement Use the switch statement to select one of many blocks of code to be executed. Syntax

JavaScript Popup Boxes Alert Box: An alert box is often used if you want to make sure information comes through to the user.When an alert box pops up, the userwill have to click "OK" to proc Syntax alert("sometext"); Confirm Box A confirm box is often used if you want the user to verify or accept something. When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed. If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false. Syntax confirm("sometext");

Prompt Box A prompt box is often used if you want the user to input a value before entering a page. When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value. If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null. Syntax prompt("sometext","defaultvalue");

JavaScript Functions To keep the browser from executing a script when the page loads, you can put your script into a function. A function contains code that will be executed by an event or by a call to the function. You may call a function from anywhere within a page (or even from other pages if the function is embedded in an external .js file). Functions can be defined both in the <head> and in the <body> section of a document. However, to assure that a function is read/loaded by the browser before it is called, it could be wise to put functions in the <head> section. How to Define a Function function functionname(var1,var2,...,varX){some code}

Events By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be detected by JavaScript. Every element on a web page has certain events which can trigger a JavaScript. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks on the button. We define the events in the HTML tags. Examples of events: A mouse click A web page or an image loading Mousing over a hot spot on the web page Selecting an input field in an HTML form Submitting an HTML form A keystroke

On Load and on Unload The onLoad event is often used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information. Some of other events onFocus, onBlur and onChange onSubmit onMouseOver and onMouseOut

Exception handling When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us there is a runtime error and asking "Do you wish to debug?". Error message like this may be useful for developers but not for users. When users see errors, they often leave the Web page. This chapter will teach you how to catch and handle JavaScript error messages, so you don't lose your audience. Try catch block try { //Run some code here }catch(err) { //Handle errors here }

Throw and throws 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)

<html><body><script type="text/javascript">var x=prompt("Enter a number between 0 and 10:","");try { if(x>10) { throw "Err1"; } else if(x<0) { throw "Err2"; } else if(isNaN(x)) { throw "Err3"; } }>

catch(er) { if(er=="Err1") { alert("Error! The value is too high"); } if(er=="Err2") { alert("Error! The value is too low"); } if(er=="Err3") { alert("Error! The value is not a number"); } }</script></body></html

Insert Special Characters The backslash ( is used to insert apostrophes, new lines, quotes, and other special characters into a text string.

JavaScriptObjects JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define your own objects and make your own variable types. Array Object

String object The String object is used to manipulate a stored piece of text. String objects are created with new String(). Syntax var txt = new String(string); or var txt = string;

RegExp Object A regular expression is an object that describes a pattern of characters. Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text. Syntax ,[object Object]

modifiers specify if a search should be global, case-sensitive, etc. ,[object Object]

The Navigator Object The Navigator object contains all information about the visitor's browser. We are going to look at two properties of the Navigator object: ,[object Object]

appVersion - holds, among other things, the version of the browser Example: <html><body><script type="text/javascript">var browser=navigator.appName;varb_version=navigator.appVersion;var version=parseFloat(b_version);document.write("Browser name: "+ browser);document.write("<br />");document.write("Browser version: "+ version);</script></body></html> OUTPUT: Browser name:Microsoft Internet Explorer Browser version:4

COOKIES A cookie is a variable that is stored on the visitor's computer. Each time the same computer requests a page with a browser, it will send the cookie too.With JavaScript, you can both create and retrieve cookie values.A cookie is often used to identify a user. Examples of cookies: ,[object Object]

Password cookie - The first time a visitor arrives to your web page, he or she must fill in a password. The password is then stored in a cookie. Next time the visitor arrives at your page, the password is retrieved from the cookie

Date cookie - The first time a visitor arrives to your web page, the current date is stored in a cookie. Next time the visitor arrives at your page, he or she could get a message like "Your last visit was on Tuesday August 11, 2005!" The date is retrieved from the stored cookie ,[object Object]

JavaScript Form Validation JavaScript can be used to validate data in HTML forms before sending off the content to a server. Javascript perform the following checks typically: ,[object Object]

whether E-mail id entered by user is valid or not

whether Date entered is valid or not

whether user has entered text in numerical format,[object Object]

with (thisform) { if (validate_required(email,"Email must be filled out!")==false) {email.focus();return false;} }}</script></head><body><form action="submit.htm" onsubmit="return validate_form(this)" method="post">Email: <input type="text" name="email" size="30"><input type="submit" value="Submit"></form></body></html>

JavaScript Objects Creating Your Own Objects There are different ways to create a new object: 1. Create a direct instance of an object The following code creates an instance of an object and adds four properties to it: personObj=new Object();personObj.firstname="John";personObj.lastname="Doe";personObj.age=50;personObj.eyecolor="blue"; 2. Create a template of an object The template defines the structure of an object: function person(firstname,lastname,age,eyecolor){this.firstname=firstname;this.lastname=lastname;this.age=age;this.eyecolor=eyecolor;} With the help of template ,we can create new instances of object like this:

EXAMPLE myFather=new person("John","Doe",50,"blue"); myMother=new person("Sally","Rally",48,"green");

Javascript

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