Conditional Operator (?:)
The 7: is the conditional operator in JavaScript, which requires three operands, hence it is called the ternary operator.
The syntax is:
var variablename=(condition) 7 valuel : value2;
In the syntax condition may be relational expression or logical expression. First condition will be evaluated, if the condition returns true then the value of the left side of the colon is assigned to the variable otherwise the value of the right side of the colon will be assigned the variable. For example,
var result=(10 > 15) ? 100 : 150;
In the above example, since the conditlon returns false the value 150 will be assigned to result.
HTML CODE:
< Html >
< Head >
< Title >Demo Program - To test Conditional 
Operator in JavaScript < /Title >
< /Head >
< Body >
< script language="javascript" type="text/
javascript" >
var valuel = 522, value2=150, value3;
value3=(valuel document.write("< br > The Value of Datal =
"+value3);
< /script >
< /Body >
< /Html >

Rules for naming variable:
a) The first character must be a letter or an underscore (-). Number cannot be as the first character.
b) The rest of the variable name can include any letter, any number, or the underscore. we can't use any other characters, including spaces, symbols, and punctuation marks.
c) JavaScript variable names are case sensitive. That is, a variable named Register Number is treated as an entirely different variable than one named registernumber.
d) There is no limit to the length of the variable name.
e) JavaScript's reserved words cannot be used as a variable name. All programming lanquaqes have a supply of words that are used internally by the language and that cannot be used for variable names.

1. Relational operators are also called as Comparison operators, they compares two values and the result is true or false.
2. JavaScript provides a rich set of relational operators including = (equal to), ! = (not equal to), < (less than), > (greater than), < = (less than or equal to), and > = (greater than or equal to). Using a relational operator in an expression causes the expression to evaluate as true if the condition holds or false if otherwise.

The syntax of alert box is
Alert(" Message ");
(or) Window.alert(" Message ");
Example:
alert (" Name is compulsory entry ");
(or) window.alert('' Name is compulsory entry ");

The prompt dialog box is displayed using a method called prompt() which takes two parameters: 
(i) a label which you want to display in the text box and
(ii) a default string !o display in the text box. This dialog box has two buttons: OK and Cancel.
If the user clicks the OK button, the prompt() will return the entered value from the text box. If the user clicks the Cancel button, the prompt () returns null.