Javascript NaN

Question

null==undefined //true
isNaN(null) //false
isNaN(undefined) //true
NaN==undefined //false
Can you please explain this?i cannot get it

Answer 1

JavaScript has both strict and type–converting comparisons. A strict comparison (e.g., === ) is only true if the operands are of the same type and the contents match. The more commonly-used abstract comparison (e.g. == ) converts the operands to the same type before making the comparison.

You should use === strict comparision
For example:
NaN === undefined # False
Null === undefined # False
NaN === Null # False

But: NaN === NaN # False

NaN is special in that it doesn't have a real value, so comparing it to itself doesn't return true. Essentially, NaN is equal to nothing, not even NaN . ... NaN is the same as boolean false . Of course false === false , so the expression evaluates to true.

Answer 2

You may consider it easy :

isNaN(null); // false

Whenever you pass a nonnumerical value as the argument of the isNaN method, it tries to convert it to a number. After conversation, if it evaluates to a number, then returns false. Otherwise returns true.

console.log(+null); // 0

A little '+' in front of anything (i.e string) makes it a number. As you can see, the conversation of null to a number is 0. And isNaN(0) is false. Therefore the final answer is false. However,

console.log(+undefined); // NaN

You can see after the conversation, it gives us NaN. And isNaN(NaN) is of course true.

The other two were explained by Muhammad :))

Answer 3

Arb Rahim Badsa Muhammad when converting both null and undefined using == give same value.but why converting using isNaN give different value or how it compare other with NaN value.while converting null to number gives 0 then why not converting undefined to number gives 0 when they have same content(null==undefined)

Answer 4

To solve those misconceptions we have Number.isNaN static method comes with EcmaScript 2015# Number.isNaN

Number.isNaN(undefined) #false

IsNaN() differs from Number.isNaN()