JavaScript - Web Programming - Lecture Slides, Slides of Computer Programming

JavaScript IS

CASE

SENSITIVE

JavaScript Semantics

 Semicolons need not terminate statements although they do no harm  Unless two statements are placed on the same line  Variables  var data type is generic  JavaScript is not strongly typed like Java  Type conversion happens on the fly  Other types  number , boolean , string , function , object

Creating a First Script

(Example)

 See JavaScriptExample1.htm

 Pay particular attention to the order in which the script code executes

Comments

 Comments appear differently inside of JavaScript block that outside of a JavaScript block  The characters // on a line mark the line as a comment  The strings /* and */ mark the begin and end of a multi-line comment

Adding Comments

**

Variables (1)

 JavaScript is “loosely typed‟  data types change dynamically as the program runs  Declare variables with the var statement

Variables (2)

 Examples

var x // Now x is undefined var x = 5; // Now x is a Number var x = "John"; // Now x is a String

Variables (3)

 Like VB, there are local and global variables  Local variables are declared inside of a procedure  Global variables are declared in a **

Calling a Function

 Functions execute when called  Call functions explicitly from other JavaScript code  Call functions implicitly from an event handler

Calling a Function (Exampple)

 From another function or from within another JavaScript block, call the function with it‟s name an parameters

 Example: ****

Returning a

Value from a Function

 Call the return statement with an argument as in

return 0;