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What is the best way to check a given variable is NaN or not?

(only using pure Javascript without any libraries such as Underscore)

siva636
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    [**isNaN**](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN) must be considered as the best way. – davidkonrad Dec 07 '15 at 04:50

2 Answers2

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JavaScript has function isNaN for that purpose. As described in w3schools:

The isNaN() function determines whether a value is an illegal number (Not-a-Number).

This function returns true if the value is NaN, and false if not.

For example:

isNaN(123) // returns false;
isNaN("Hello")  //returns true
dotnetom
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You can use isNaN(x) which returns a boolean value (true if x is NaN, false otherwise).