2. ECMAScript

• A Web browser is considered a host environment for ECMAScript, but it is not the only host environment.
•  ECMAScript describes the following:

❑ Syntax

❑ Types 

❑ Statements 

❑ Keywords 

❑ Reserved Words 

❑ Operators 

❑ Objects

ECMAScript is simply a description, defining all the properties, methods, and objects of a scripting language. Other languages implement ECMAScript, as JavaScript does (see Figure 1-2), as the baseline for functionality.  

ECMAScript is separated into editions rather than versions because it is defined in a standard called ECMA-262. Like any standard, ECMA-262 can be edited and updated.  
Today, all popular Web browsers comply with the third edition of ECMA-262.

Syntax

• Everything is case-sensitive. Just as with Java, variables, function names, operators, and everything else is case-sensitive, meaning that a variable named test is different from one named Test.
• Variables are loosely typed. Unlike Java and C, variables in ECMAScript are not given a specific type. Instead, each variable is defined using the var operator and can be initialized with any value. This enables you to change the type of data a variable contains at any point in time (although you should avoid doing so whenever possible). 

             Some examples: 

                        var color = “red”;

                        var num = 25;

                        var visible = true; 

• End-of-line semicolons are optional.

             Example: 

                        var test1 = “red”

                        var test2 = “blue”;

• Comments are the same as in Java, C, and Perl.

           //this is a single-line comment

           /* this is a multiline comment */

• Braces indicate code blocks.

if(condition){

              //I'm in a block
          }

Variables

var is used.

var a;

var b = 1, c =3, d = 'ffff';

//Example

var str = "I am a string";  //type of str variable is string;

str = 56;  //assigned a number to str;

alert(str); //results in "56", now its type changed from "string" to "number"! coz its loosely-typed.

• The first character must be a letter, an underscore (_), or a dollar sign ($).
• All remaining characters may be underscores, dollar signs, or any alphanumeric characters.
• Camel Notation. Ex: var channelName; //I suggest the reader to prefer this notation.
• Pascal Notation. Ex: var ChannelName;
• Hungarian Notation. Ex: var iChannelName; //i denotes integer. we will not discuss this notation in detail.