Why is NaN === NaN false? [duplicate]

Solution 1:

Strict answer: Because the JS spec says so:

• If Type(x) is Number, then
  • If x is NaN, return false.
  • If y is NaN, return false.

Useful answer: The IEEE 754 spec for floating-point numbers (which is used by all languages for floating-point) says that NaNs are never equal.

Solution 2:

This behaviour is specified by the IEEE-754 standard (which the JavaScript spec follows in this respect).

For an extended discussion, see What is the rationale for all comparisons returning false for IEEE754 NaN values?

Solution 3:

Although either side of NaN===NaN contains the same value and their type is Number but they are not same. According to ECMA-262, either side of == or === contains NaN then it will result false value.

you may find a details rules in here-

http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3