NaN Bug and Solution in Javascript

Javascript is very beautiful and growing language. It has some in-built bugs.

NaN — Not a Number

Everyone well known NaN is Not a Number. But its not accurate. We can say NaN is Bad Number or failed Number than the Not a Number.

var x = 10/ 'foo'; //NaN
typeof x // 'number'

x is not a number but the typeof x is return number. But x has the NaN. Its too misleading behavior. And we cant validate directly

x == NaN; //false

Solution

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Javascript has one built in method called isNaN. So we can use that method to validate this variable.

isNaN(x) // true

Is problem solved. Nope.

var y= 'foo';
isNaN(y); //true

variable y is not a number, but value is not NaN. How can handle this kind of situation?

We have the option in ES6

Number.isNaN(y);

or we can write the polyfill

if(!Number.isNaN(y)) {
   Number.isNaN = function(n) {
      return n !== n;
   }
}