Name
isNaN( ) Global Function — equality test for the special NaN
value
Availability
Flash 5
Synopsis
isNaN(value)
Arguments
- value
The expression to test.
Returns
A Boolean value: true
if
value
is the special numeric value
NaN
; otherwise, false
.
Description
To test whether or not a value is equal to the special numeric value
NaN
, we must use the isNaN( )
function because NaN
does not test equal to itself
in an ordinary equality test. For example, the expression:
NaN == NaN;
yields the value false
. The isNaN(
)
function is often used to check whether a mathematical
error (such as zero divided by itself) has occurred in a phrase of
code or whether converting a value to a legitimate number has failed.
Because isNaN( )
returns true
when the expression is not a valid numeric
expression, you’ll often use the logical NOT operator
(!
) along with isNaN( )
(something that is not not a number
is a number). Note that 0/0 yields
NaN
, but all positive numbers divided by
yield Infinity
, and all negative numbers divided
by
yield -Infinity
.
Example
// Set a value var x = "test123"; // Check if x is a legitimate number before using it is in a math expression. // This is a handy technique for user input in text fields, which always a string. if (!isNaN(parseFloat(x))) { var y = parseFloat(x) * 2; }
See Also
isFinite( ), NaN
; Section 4.3.3 in Chapter 4
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