Writing JScript Code

Like many other programming languages, Microsoft JScript is written in text format, and is organized into statements, blocks consisting of related sets of statements, and comments. Within a statement you can use variables, immediate data such as strings and numbers, and expressions.

Statements

A JScript code statement consists of one or more items and symbols on a line. A new line begins a new statement, but it is a good idea to terminate your statements explicitly. You can do this with the semicolon (;), which is the JScript termination character.

aBird = "Robin";
var today = new Date();

A group of JScript statements that is surrounded by braces ({}) is called a block. Blocks of statements are used, for example, in functions and conditionals.

In the following example, the first statement begins the definition of a function, which consists of a block of five statements. The last three statements, which are not surrounded by braces, are not a block and are not part of the function definition.

function convert(inches)  {
    feet = inches / 12;  //  These five statements are in a block.
    miles = feet / 5280;
    nauticalMiles = feet / 6080;
    cm = inches * 2.54;
    meters = inches / 39.37;
}
km = meters / 1000;  //  These three statements are not in a block.
kradius = km;
mradius = miles;

Comments

A single-line JScript comment begins with a pair of forward slashes (//). A multiline comment begins with a forward slash and asterisk in combination (/*), and ends with the reverse (*/).

aGoodIdea = "Comment your code thoroughly.";  //  This is a single-line comment.

/*
This is a multiline comment that explains the preceding code statement.

The statement assigns a value to the aGoodIdea variable. The value, which 
is contained between the quote marks, is called a literal. A literal explicitly 
and directly contains information; it does not refer to the information indirectly. 
(The quote marks are not part of the literal.)
*/

//  This is another multiline comment, written as a series of single-line comments.
//  After the statement is executed, you can refer to the content of the aGoodIdea
//  variable by using its name, as in the next statement, in which a string literal is
//  appended to the aGoodIdea variable by concatenation to create a new variable.

var extendedIdea = aGoodIdea + " You never know when you'll have to figure out what it does.";

Assignments and Equality

The equal sign (=) is used in JScript to indicate the action of assigning a value. That is, a JScript code statement could say

anInteger = 3;

It means "Assign the value 3 to the variable anInteger," or "anInteger takes the value 3." When you want to compare two values to find out whether they are equal, use a pair of equal signs (==). This is discussed in detail in Controlling Program Flow.

Expressions

A JScript expression is something that a person can read as a Boolean or numeric expression. Expressions contain symbol characters like "+" rather than words like "added to". Any valid combination of values, variables, operators, and expressions constitutes an expression.

var anExpression = "3 * (4 / 5)";
var aSecondExpression = "Math.PI * radius * 2";
var aThirdExpression = aSecondExpression + "%" + anExpression;
var aFourthExpression = "(" + aSecondExpression + ") % (" + anExpression + ")";