NaN

In computing, NaN stands for Not a Number. It means the result of input is or unrepresentable. For example, division by zero in most Programming language returns NaN. Systematic use of NaN was introduced by the IEEE 754 in 1985, along with the other numbers such as infinities.
In JavaScript.
In JavaScript, or returns . using also returns . You can use or to check if a value is NaN. there is difference between two functions. the returns when the value is NaN when parsed to int. but returns when the value is currently NaN.
For example: