The isNaN() function converts the argument to a number and returns true if the result is NaN (Not-a-Number), or false if the result is a valid number or can be converted to one. This means that isNaN() can be unreliable for checking if a value is NaN because it coerces the argument to a number before checking.

On the other hand, Number.isNaN() is a method that returns true if the argument is NaN and false if it is a valid number or any other type of value. It does not perform type coercion, so it will only return true if the value passed as an argument is actually NaN.

Another difference is that isNaN() can be overwritten, as it is a property of the global object. However, Number.isNaN() is a static method of the Number object and cannot be overwritten.
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