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isNaN() global function

You cannot rely on the equality (==) and strict equality (===) comparison operators of the Nan global property to find out whether a value is Nan or not

For this reason we have the isNaN() global function to test for Nan.

  • Be aware that some results using the isNaN() function are unreliable as demonstrated in the example, so use this function with care.

Description

The isNaN global function is used to determine whether a value is NaN (Not-A-Number).

Syntax


Signature Description
isNaN(testValue)Global function is used to determine whether a value is NaN (Not-A-Number).

Parameters


Parameter Description
testValueThe value to be tested.

Below are some examples showing usage of the isNaN() function.

// isNaN.
var isNaNValues = new Array(5);
isNaNValues[0] = isNaN(17); // number so false
isNaNValues[1] = isNaN('17'); // string number so false
isNaNValues[2] = isNaN(17.2345); // float number so false
isNaNValues[3] = isNaN(NaN); // isNaN is NaN so true
*/
 / The next test shows why isNan is unreliable.
 / 1) Parsing 'aaa' as a number fails and so Nan is returned
 / 2) As you can see from the example above isNaN(NaN) returns true
 / 3) Therefore parsing a string that cannot be converted to a numeric gives a 
 /    double positive and makes isNaN() unreliable in this situation.
 /*
isNaNValues[4] = isNaN('aaa');
alert(isNaNValues);

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Related Tutorials

JavaScript Intermediate Tutorials - Lesson 6 - More Maths Functions



  

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