HTML and CSS Reference
InDepth Information
Working with Operators and Operands
In the previous session, you worked with
Date
objects to display specified dates and
times on a Web page. In this session, you'll learn how to perform calculations with dates
and JavaScript variables. To perform a calculation, you need to insert a JavaScript state
ment that contains an operator. An
operator
is a symbol used to act upon an item or a
variable within an expression. The variables or expressions that operators act upon are
called
operands
. An operator is a very basic concept. In fact, you've been using opera
tors throughout this and the previous tutorial. You've been using the
+
operator to com
bine text strings and add numeric values. For example, the following statement from the
showDate() function uses the
+
operator along with the
getMonth()
method to increase
the month number value by 1:
thisMonth = dateObj.getMonth() + 1;
You have also used the
+
operator to combine text strings, as in the following state
ment from the showDate() function, which displays dates in the month/day/year format:
thisMonth + “/” + thisDate + “/” + thisYear;
Using Arithmetic and Unary Operators
The
+
operator belongs to a group of operators called
arithmetic operators
that perform
simple mathematical calculations. Figure 1113 lists some of the arithmetic operators
and gives examples of how they work.
Figure 1113
arithmetic operators
Operator
Description
Example
+
Combines or adds two items
Men = 20;
Women = 25;
Total = Men + Women;

Subtracts one item from another
Income = 1000;
Expense = 750;
Profit = Income  Expense;
*
Multiplies two items
Width = 50;
Length = 20;
Area = Width * Length;
/
Divides one item by another
Persons = 50;
Cost = 200;
CostPerPerson = Cost / Persons;
%
Calculates the remainder after
dividing one value by another
TotalEggs = 64;
CartonSize = 12;
EggsLeft = TotalEggs % CartonSize;
The arithmetic operators shown in Figure 1113 are also known as
binary operators
because they work with two operands in an expression. JavaScript also supports
unary
operators
, which work on only one operand. Unary operators can make code more
compact and efficient. One of the unary operators is the
increment operator
, which
increases the value of the operand by 1. The increment operator is indicated by the
++
symbol. For example, the following two expressions both increase the value of the
x
vari
able by 1; the first uses the binary operator indicated by the
+
symbol, and the second
uses the increment operator indicated by the
++
symbol:
x = x + 1;
x++;