HTML and CSS Reference
Working with Data Types
So far, the examples you've explored have used variables that store text strings. However,
• numeric value
• text string
• Boolean value
• null value
A numeric value is any number, such as 13, 22.5, or -3.14159. Numbers can also be
expressed in scientific notation, such as 5.1E2 for the value 5.1 × 10 2 (or 510). Numeric
values are specified without any quotation marks. Thus, if you wished to store the value
2007 in the year variable, you would use the statement
A text string is any group of characters, such as Hello or Happy Holidays! or 421
Sunrise Lane . Text strings must be enclosed within either double or single quotation
marks, but not a mix of both. The string value 'Hello' is acceptable, but the string value
“Hello' is not.
A boolean value indicates the truth or falsity of a statement. There are only two
Boolean values: true and false . For example, the following statement sets the value of the
useSafari variable to true and the value of the useIE variable to false :
Boolean values are most often used in programs that must act differently based on
different conditions. The useSafari variable cited above might be used in a program that
tests whether a user is running the Safari browser. If the value is set to true , the program
might be written to run differently for the user than if the value were set to false .
Finally, a null value indicates that no value has yet been assigned to a variable. This
can be done explicitly using the keyword null in assigning a value to a variable, as in the
If a Boolean variable's
value is left undefined, it is
as having a value of false .
or implicitly by simply declaring the variable without assigning it a value, as follows:
In either case, the emLink variable would have a null value until it was assigned a
value using one of the other data types.
used. This means that a variable can switch from one data type to another within a single
program. In the following two statements, the Month variable starts out as a numeric
variable with an initial value of 5, but then becomes a text string variable containing the
cific data types, is referred to as a weakly typed language . Some other programming lan-
guages, known as strongly typed languages , force the programmer to explicitly identify a
variable's data type. In those languages, the above code would result in an error because
a given variable would not be able to switch from one data type to another.