Boolean Values
The number and string
data
types have a large or infinite number of possible values. The boolean
data type, on the other hand, has only two. The two legal boolean
values are represented by the literals true
and
false
. A boolean value represents a truth
value -- it says whether something is true or not.
Boolean values are generally the result of comparisons you make in your JavaScript programs. For example:
a == 4
This code tests to see if the value of the variable
a
is equal to the number 4
. If
it is, the result of this comparison is the boolean value
true
. If a
is not equal to
4
, the result of the comparison is
false
.
Boolean values are typically used in JavaScript control structures.
For example, the
if/else
statement in JavaScript performs one
action if a boolean value is true
and another
action if the value is false
. You usually combine
a comparison that creates a boolean value directly with a statement
that uses it. The result looks like this:
if (a == 4) b = b + 1; else a = a + 1;
This code checks if a
equals 4
.
If so, it adds 1
to b
;
otherwise, it adds 1
to a
.
Instead of thinking of the two possible
boolean values as
true
and false
, it is sometimes
convenient to think of them as on
(true
) and off
(false
) or yes
(true
) and no
(false
). Sometimes it is even useful to consider
them equivalent to 1
(true
) and
0
(false
). (In fact, JavaScript
does just this and converts true
and
false
to 1
and
0
when necessary.)[7]
[7] C programmers should note that JavaScript ...
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