WTP Unit 4 JavaScript and DHTML

Javascript: – Client side scripting, – What is Javascript, – How to develop Javascript, – Simple Javascript, – Variables, – Functions, – Conditions, – Loops and repetition, – Javascript: Advance script, Javascript and objects, – Javascript own objects, – The DOM and web browser environments, – Forms and validations DHTML : – Combining HTML, CSS and Javascript, – Events and buttons, – Controlling your browser

Client-side Scripting Client-side scripts, which run on the user’s workstation can be used to: –Validate user inputs entered on HTML forms –Create advanced Web page features, including: Handling manipulation of the browser (opening new ones, redirection …) Creating “cookies” that store data on user’s computer about his or her actions while browsing a Web page Create animations and graphical effects

JavaScript Can be Server-side scripting language too Can be added to standard HTML Web pages using special HTML tags Used in Web pages for data validation Used to create pop-up browser windows Animations, games, dynamic graphics

JavaScript has three parts 1)Core: Includes operators, expressions, statements and subprograms 2)Client-side: Collection of objects which can control over browser and user-browser interaction is possible 3)Server-side: Collection of objects using to access the database on the server

Java vs. JavaScript JavaJavaScript Programming languageScripting language,Interpreted (not compiled) Object oriented languageNO Strongly typed, type checking is done at compile time Weakly typed, checking the compatibility of type can be done dynamically

Where to put your script? –JavaScript programs can be used in two ways: Incorporated directly into an HTML file –Using tag Placed in an external (source) file –Has file extension.js –Contains only JavaScript statements –Using

Advantages of a JS Source File Makes HTML document neater (less confusing) JS can be shared among multiple HTML files Can use a combination of embedded and non–embedded code

How to write? Placing JavaScript in or sections –Script statements interpreted in order of document rendering – section rendered before section Good practice to place as much code as possible in section

A JavaScript Program in Head Tag A First Program in JavaScript document.write(“Hello world ! – From body Tag.” );

A JavaScript Program in Body tag A First Program in JavaScript document.write( “Hello world ! – From Head Tag.” );

Reserved Words Special words associated with special meaning 1.break 2.case 3.catch 4.do 5.default 6.for 7.function 8.new 9.return 10.throw 11.var 12.void

Variables Names given to variables, holds data value 1.Variables begins with either letter, underscore or dollar sign 2.No limit on the length 3.Case-sensitive – VVP x VvP x vVP

Variable Declaration No data type is required. Example, declaring variables within a Script: var variable1; var variable1,variable2; Example, initialising variables within a Script: variable1 = 0; variable2 = “Hello”;

Primitives types (Variables)

Functions JavaScript, like a lot of programming languages, uses functions. The basic format is : function function-name ( parameters ) { lines of code }

Function Example function myFunction() { return ("Hello, have a nice day!") } The script in the body section calls a function. The function returns a text. document.write(myFunction())

CONVERTING AND EVALUATING VARIABLES AND EXPRESSIONS parseInt – convert string to int parseFloat – convert string to float eval – convert string to numbers

Dialog Boxes alert() used to display message. prompt() allows user enter something. confirm() used to get user confirmation.

1 ALERT DIALOG BOX – The Alert dialog box is used to display some textual information on the web browser. – The dialog box will have only one button ‘OK’. – Example alert(“Hi, How are You");

2 CONFIRM DIALOG BOX A confirm box is often used if you want the user to verify or accept something. A confirm box display the predefine message and ‘OK’ and ‘CANCEL’ button. Example if(confirm(“Do you want to accept it?")) document.write(“You pressed ok")

3 PROMPT DIALOG BOX A prompt box is often used if you want the user to input a value before entering a page. A prompt box display a predefine message, a textbox for user input and display ok and cancel button. Example name = prompt("Enter your name", "First name") document.write("Welcome " + name)

IF statements if (condition) { //statements1 } else { //statements2 } SWITCH statement switch (expression){ case label : statement; break; case label : statement; break; default : statement; }

Loops & Repetition DO WHILE statement Do { } while(condition) WHILE statement while (condition) { statements } FOR statement for ([initial-expression]; [condition]; [increment-expression]) { //statements }

User-Defined Objects JavaScript is an Object Based Scripting language. JavaScript allows you to define your own objects and make your own variable types. Note that an object is just a special kind of data. An object has properties and methods.

Object: Properties Properties are the values associated with an object. In the following example we are using the length property of the String object to return the number of characters in a string: var txt="Hello World!"; document.write(txt.length);

Object: Methods Methods are the actions that can be performed on objects. In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters: var str="Hello world!"; document.write(str.toUpperCase());

JavaScript Objects A person is an object. Properties are the values associated with the object. The persons' properties include name, height, weight, age, skin tone, eye color, etc. All persons have these properties, but the values of those properties will differ from person to person. Objects also have methods. Methods are the actions that can be performed on objects. The persons' methods could be eat(), sleep(), work(), play(), etc.

DOM and Web Browser Environments What is the DOM? The Document Object Model is an API for HTML and XML documents. It provides a structural representation of the document, enabling you to modify its content and visual presentation. Essentially, it connects web pages to scripts or programming languages. It defines the logical structure of documents and the way a document is accessed and manipulated. With the Document Object Model, programmers can build documents, navigate their structure, and add, modify, or delete elements and content.

A graphical representation of the DOM of the example table is:

The Document Object Model Root level of the JavaScript DOM is the window object Window objects have properties such as status line The next level up is the document object…which is the loaded HTML page Document objects have properties such as background colour Each HTML element (e.g. links or forms) is a property of the document object.

Javascript Document Object Model

Document properties The first image on a web page can be represented as the property document.images[0] A web form also has its properties accessible in the object tree You can find any property by tracing it through the tree: document.forms[0].elements[0]

Events It describes actions that occur as a result of user interaction with the web page or other browser related activities. Example : When a button is clicked or a mouse has been moved or even when a key has been pressed an event is said to be occurred. Events are built into the HTML code, not within script tags. Multiple events can be active

Events & Functions function myfunction() { alert("HELLO"); } By pressing the button, a function will be called. The function will alert a message.

Controlling your browser How to Scroll a Page With JavaScript This example demonstrates how to use the JavaScript scrollBy and setTimeout methods to make a web page scroll down automatically. function pageScroll() { window.scrollBy(0,50); // horizontal and vertical scroll increments scrolldelay = setTimeout('pageScroll()',100); // scrolls every 100 milliseconds }

Controlling your browser To being scrolling automatically when the page loads, add the following code to the body tag: To begin scrolling when prompted by the user, call the function from a link or button: Text Link Scroll Page Scroll Page (Note: If you click this link, you'll need to click the link at the bottom of the page to cancel the scrolling)

Controlling your browser Button Stop Scrolling The pageScroll() function causes the page to keep scrolling forever. The following function will stop the scrolling, and can be called in the same way: function stopScroll() { clearTimeout(scrolldelay); } Stop Scrolling

Controlling your browser Scroll Directly to a Particular Point Use the scroll() method to jump to a particular point on the page. The target position is specified in pixels from the top left corner of the page, horizontally and vertically. function jumpScroll() { window.scroll(0,150); // horizontal and vertical scroll targets } Jump to another place on the page

GTU Questions What do you mean by event in JavaScript? Give at least two examples of events with their handling. (GTU-2011 May)07 Write a JavaScript program to print first N odd numbers divisible by 07 (GTU-2011 May) Answer the following questions with respect to JavaScript Give the different purpose for which Javascripts are used. 2. Writing user defined objects in JavaScript. (GTU-2011 May) Write an HTML form accepting an integer having 4-digits. Provide 07 necessary validations using JavaScript. Input should not accept characters. (GTU-2011 May) Write a program using Java Script, which sorts elements of an array in descending order using bubble sort. (GTU-2011 Nov)07

What are objects in Java Script? Explain properties, methods and 07 event of window object of Java Script. (GTU-2011 Nov) Create a HTML page with Java Script, which takes one integer number as input and tells whether the number is even or odd. 07 (GTU-2011 Nov) What is JavaScript ? Explain Variable Scope and assignment with Example. (GTU-2013) 07 Create HTML Page with JavaScript which takes Integer number as input and tells whether the number is Prime or Not. (GTU-2013) 07 Create HTML Page with JavaScript which takes Integer number as input and tells whether the number is ODD or EVEN. (GTU-2013) 07 Explain Array, Function with Example (with reference to JavaScript).(GTU-2013) 07

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