Name
isNaN( ): check for not-a-number â ECMAScript v1
Synopsis
isNaN
(x
)
Arguments
-
x
The value to be tested.
Returns
true
if
x
is (or can be converted to) the
special not-a-number value; false
if x
is
any other value.
Description
isNaN( )
tests its
argument to determine whether it is the value NaN
, which represents an illegal number (such as the
result of division by zero). This function is required because
comparing a NaN
with any value,
including itself, always returns false
, so it is not possible to test for
NaN
with the ==
or ===
operators.
A common use of isNaN( )
is
to test the results of parseFloat(
)
and parseInt( )
to
determine if they represent legal numbers. You can also use isNaN( )
to check for arithmetic errors,
such as division by zero.
Example
isNaN(0); // Returns false isNaN(0/0); // Returns true isNaN(parseInt("3")); // Returns false isNaN(parseInt("hello")); // Returns true isNaN("3"); // Returns false isNaN("hello"); // Returns true isNaN(true); // Returns false isNaN(undefined); // Returns true
See Also
isFinite( )
, NaN
, Number.NaN
, parseFloat( )
, parseInt( )
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