JavaScript Tutorials - Herong's Tutorial Examples - 2.33, by Herong Yang
Declaring Variables - "var" Statements
This section provides descriptions on variables and a tutorial example on how to declare variables with 'var' statements.
What are variables? Variables are symbolic names that refer to values stored in the memory.
Variable names must be sequences of alphanumeric characters and underscore (_). But the first character can not be a numeric character. (_5star) is a valid variable name. But (5star) is not an invalid variable name.
Variable can be used without declaration. But it is strongly recommended that all variables are declared with "var" statements in the following syntax formats:
var var_name_1; var var_name_1 = value_1; var var_name_1, var_name_2, var_name_3, ...; var var_name_1 = value_1, var_name_1 = value_1, ...;
If a variable is declared without initial value, it contains the "undefined" value.
Here is a JavaScript tutorial example that shows you how to declare variables with "var" statements:
<html> <!-- Variables.html Copyright (c) 2002 HerongYang.com. All Rights Reserved. --> <head><title>Variables</title></head> <body> <pre> <script type="text/javascript"> var site_url = 'herongyang.com'; var site_rank = 9; var site_content; site_title = "Herong's Tutorial Examples"; // should be declared first document.write(site_url); document.write('\n'); document.write(site_title); document.write('\n'); document.write(site_rank); document.write('\n'); document.write(site_content); document.write('\n'); </script> </pre> </body> </html>
The output of this sample JavaScript is:
herongyang.com Herong's Tutorial Examples 9 undefined
Table of Contents
ECMAScript Language Specification and JavaScript Dialects
►Data Types, Variables and Expressions
Primitive Data Types - Numbers, Strings, and Booleans
►Declaring Variables - "var" Statements
Operators and Expressions - Examples
Creating, Accessing, and Manipulating Arrays
Defining and Calling Functions
Web Browser Supporting JavaScript
Server-Side and Client-Side Web Scripting
Defining Your Own Object Types
Inheritance of Properties and Methods through the Prototype Object Chain
'jrunscript' - JavaScript Shell Command from JDK
Using Functions as "Function" Objects
Introduction to Built-in Object Types
W3C's Document Object Model (DOM) Specifications