NaN - It's Not A Number

According to MDN,

NaN is a property of the global object. In other words, it is a variable in global scope.

The initial value of NaN is Not-A-Number the same as the value of Number.NaN. In modern browsers, NaN is a non-configurable, non-writable property. Even when this is not the case, avoid overriding it. It is rather rare to use NaN in a program.

Hear the value of NaN is Number.NaN. But, wait!

NaN === Number.NaN // false

Maybe because of the type you think

NaN == Number.NaN // false

Somewhat reasonable explanation started here when I followed the links.

With a lot of confusion around NaN, let us see how we could arrive at a value of NaN.
There are 5 different operations which could result in NaN.

• Numbers that can't be parsed

parseInt('Integer')  NaNNumber('%^@#')  NaN

• Math operation where the result is not a real number

Math.sqrt(-1);  NaN

• The operand of an argument is NaN

NaN + 20  NaN60 * NaN  NaN

• Indeterminate form

0 * Infinity  NaN

• Any operation that involves a string and is not an addition operation

"Integer" * 5  NaN

For geekier discussions, reach out to me on twitter at @radnerus93, DM always open.