TUTORIAL 10: PROGRAMMING WITH JAVASCRIPT Session 2: What is JavaScript?

Objectives  What is JavaScript?  What can JavaScript do?  JavaScript – How to  Writing JavaScript Statements  JavaScript – Where to  Writing JavaScript Comments  Declaring Variables in JavaScript

What is JavaScript?  JavaScript was designed to add interactivity to HTML pages  JavaScript is a scripting language  A scripting language is a lightweight programming language  JavaScript is an interpreted language (means that scripts execute without preliminary compilation)  Everyone can use JavaScript without purchasing a license

What can JavaScript do? JavaScript gives HTML designers a programming tool  JavaScript can read and write HTML elements  JavaScript can react to events  JavaScript can change HTML content  JavaScript can change HTML images  JavaScript can change HTML styles  JavaScript can be used to validate data

Example of JavaScript Use

Other Examples of JavaScript Uses  htm htm 

JavaScript – How to..  A JavaScript program can be placed directly in an HTML file or it can be saved in an external text file  Insert a client-side script in a Web page when using the script element script commands

JavaScript: Script Element  In Class Example  Writing to the HTML document  Changing HTML elements

JavaScript Statements  JavaScript is a sequence of statements to be executed by the browser.  JavaScript is case-sensitive.  A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do.  Example: document.write("Hello Dolly");

JavaScript Statements  In Class Examples  JavaScript Code  JavaScript Code Block (use of a function)

JavaScript – Where to..  JavaScript can be put in the and in the sections of an HTML page.  JavaScript can be embedded in the HTML code.  JavaScript can also be placed in external files.

JavaScript: in head, body, and external  In Class Examples  In body  In head  External JavaScript file

JavaScript Comments  Commenting your code is an important programming practice // comment text for a single line /* comment text for multiple lines

JavaScript Comments  In-Class Example:  Add a single-line comment  Add a multi-line comment

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 carname.  Rules for JavaScript variable names:  Variable names are case sensitive (y and Y are two different variables)  Variable names must begin with a letter, the $ character, or the underscore character

Declaring JavaScript Variables  Declaring a variable tells the JavaScript to reserve memory space for the variable.  To declare a JavaScript variable, use the statement var variable; where variable is the name assigned to the variable.  To declare a JavaScript variable and set its initial value, use var variable = value; where value is the initial value of the variable.

Declaring JavaScript Variables  JavaScript data types:  Numeric values  Text strings  Boolean values  Null values  You must declare a variable before using it.

Declaring JavaScript Variables  Numeric value is any number, such as 13, 22.5, etc.  Text string is any group of text characters, such as “Hello” or “Happy Holidays!”  Must be enclosed within either double or single quotations (but not both)  Boolean values accept only true and false values  Null value has no value at all

Declaring Variables  In Class Example