Creating a function to calculate age using Function Expression

Implement the getAge() function that takes a birth date as an argument and returns the calculated age. The function should be declared using a Function Expression. Example usage:

const calculateAge = function(birthDate) {
    // implementation
};

const age = calculateAge(new Date('1990-05-15'));
console.log(age); // outputs the current age

The function should work correctly with dates in both the past and the future, taking leap years into account.