CODEWITHSUNDEEP
javascriptnan
lock
lock

Reputation: 6614

what is the reserved keyword for NaN in javascript?

if i want to test the result of an expression and the function would return NaN how would i check that?
examples:
$('amount').value.toInt()!='NaN'
^ does not work and i assume that the returned value is not a string,
$('amount').value.toInt()!=NaN
^ doesnt seem to work either and this one seems obvious

so how do i check wether the returned value is not a number?

Upvotes: 8

Views: 2132

Answers (3)

Miles
Miles

Reputation: 32468

The NaN value is defined to be unequal to everything, including itself. Test if a value is NaN with the isNaN() function, appropriately enough. (ECMAScript 6 adds a Number.isNan() function with different semantics for non-number arguments, but it's not supported in all browsers yet as of 2015).

There are two built-in properties available with a NaN value: the global NaN property (i.e. window.NaN in browsers), and Number.NaN. It is not a language keyword. In older browsers, the NaN property could be overwritten, with potentially confusing results, but with the ECMAScript 5 standard it was made non-writable.

  • As @some pointed out in the comments, there is also the global function isFinite() which may be useful.

Upvotes: 37

ismnoiet
ismnoiet

Reputation: 4159

the best way to check the result of numeric operation against NaN is to aproach this way , example:

var x  = 0;
var y  = 0;
var result = x/y;  // we know that result will be NaN value
// to test if result holds a NaN value we should use the following code :

if(result !=result){
console.log('this is an NaN value');
}

and it's done.

the trick is that NaN can't be compared to any other value even with it self(NaN !=NaN is always true so we can take advantage of this and compare result against itself)

this is JavaScript(a good and bizarre language)

Upvotes: 2

Hemerson Varela
Hemerson Varela

Reputation: 25792

Equality operator (== and ===) cannot be used to test a value against NaN. Use Number.isNaN() or isNaN() instead.

NaN === NaN;        // false
Number.NaN === NaN; // false
isNaN(NaN);         // true
isNaN(Number.NaN);  // true

Upvotes: 1

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