JavaScript’s `isNaN()` function is a global function used to determine if a value is Not-a-Number (NaN). NaN is a special numeric value that represents an invalid number. It is often returned by mathematical operations that cannot be performed, such as dividing by zero or taking the square root of a negative number.
To use `isNaN()`, simply pass the value you want to check as an argument to the function. The function will return `true` if the value is NaN, and `false` otherwise.
