NumberisNaN

NumberisNaN is a JavaScript function that determines whether a value is NaN (Not-a-Number). NaN is a special numeric value that represents an undefined or unrepresentable result of a numeric operation. For example, dividing zero by zero results in NaN, as does attempting to convert a non-numeric string to a number using `parseInt` or `parseFloat` without a valid number at the beginning.

The `Number.isNaN()` method is the preferred way to check for NaN in JavaScript. It returns `true` if the value is NaN, and `false` otherwise. It's important to note that `Number.isNaN()` only returns true for the actual NaN value. It does not coerce its argument to a number before checking. This is a key difference from the global `isNaN()` function.

The global `isNaN()` function, while serving a similar purpose, has a quirk: it attempts to convert its argument to a number first. If the conversion results in NaN, it returns `true`. This means that `isNaN('hello')` returns `true` because 'hello' cannot be converted to a number, while `Number.isNaN('hello')` returns `false`. Therefore, `Number.isNaN()` is generally more reliable for precisely identifying the NaN value itself, avoiding unexpected results when dealing with non-numeric types.