Javascript Nan

javascript

// Problem with NaN:
The NaN property represents a value that is “not a number”. This special value 
results from an operation that could not be performed either because one of the 
operands was non-numeric (e.g., "abc" / 4), or because the result of the 
operation is non-numeric (e.g., an attempt to divide by zero).
Although NaN means “not a number”, its type is, believe it or not is 'number'.
NaN compared to anything – even itself! – is false.  
A semi-reliable way to test whether a number is equal to NaN is with the 
built-in function isNaN(), but even using isNaN() is an imperfect solution.

Dividing zero by zero results in a NaN — but dividing other numbers by zero does 
not.

isNaN(NaN);       // true
isNaN(undefined); // true
isNaN({});        // true
isNaN(true);      // false
isNaN(null);      // false
isNaN(37);        // false
isNaN("37");      // false: "37" is converted to the number 37 which is not NaN
isNaN("37.37");   // false: "37.37" is converted to the number 37.37 which is not NaN
isNaN("123ABC");  // true:  parseInt("123ABC") is 123 but Number("123ABC") is NaN
isNaN("");        // false: the empty string is converted to 0 which is not NaN
isNaN(" ");       // false: a string with spaces is converted to 0 which is not NaN

// dates
isNaN(new Date());                // false
isNaN(new Date().toString());     // true

// This is a false positive and the reason why isNaN is not entirely reliable
isNaN("blabla")   // true: "blabla" is converted to a number. 
                  // Parsing this as a number fails and returns NaN

ES6 offers a new Number.isNaN() function, which is a different and more reliable 
than the old global isNaN() function.

A better solution would either be to use value !== value, which would only 
produce true if the value is equal to NaN.