Why Does `typeof NaN` Return \'number\'?

Why Does typeof NaN Return 'number'?

It may seem paradoxical that a value labeled as "Not a Number" (NaN) is treated as a number by the typeof operator. However, this behavior stems from the underlying nature of NaN.

Firstly, NaN is a numeric type, despite its name. It represents an invalid or undefined numerical value. While all numbers are approximations and subject to limitations, NaN is a specific instance of a numeric value that cannot be represented accurately.

Secondly, NaN is not equal to any other value, including itself. This is because NaN is not a specific value but rather a placeholder for an invalid or undefined result. Thus, comparing NaN to itself or any other value will always return false.

Understanding the Explanation in Layman's Terms

A comparison with NaN always returns an unordered result:

NaN is not equal to any number, including itself. This means that even comparing NaN to itself will result in false.

Signalling and non-signalling comparison predicates:

Some comparison operations, such as less than or greater than, can either throw an exception or return false when dealing with NaN. These operations are known as signalling and non-signalling predicates.

Testing for NaN using equality and inequality:

Since equality and inequality tests are non-signalling, they will not throw exceptions. If a regular number is tested for equality with itself, it will always return true. However, if a NaN is tested for equality with itself, it will always return false. This provides a convenient way to detect NaN values "quietly."

The above is the detailed content of Why Does `typeof NaN` Return \'number\'?. For more information, please follow other related articles on the PHP Chinese website!