函数内部的Javascript函数-对参数感到困惑

Question

Hi everyone, I'm in the process of learning Javascript and I'm confused about having a function inside another function, in particular the argument part.

I've included a sample code from the lesson where it's looking to calculate the years until retirement for three people given their year of birth.

What I'm confused about is the year within the function yearUntilRetirement(name, year ).

Shouldn't this be yearOfBirth instead of year since it's looking back at the calculateAge(yearOfBirth) function to find the age? Or is this argument only unique to the function it is currently in?

function calculateAge(yearOfBirth) {
    var age = 2016 - yearOfBirth;
    return age;
}

function yearsUntilRetirement(name, year) {
    var age = calculateAge(year);
    var retirement = 65 - age;
    console.log(name + ' retires in ' + retirement + ' years.');
}

yearsUntilRetirement('John', 1990);
yearsUntilRetirement('Mike', 1969);
yearsUntilRetirement('Mary', 1948);

Answer 1

Maybe this will clarify.

When you call yearsUntilRetirement(name, year) , you pass in two values as the arguments. Such as yearsUntilRetirement("John", 1975) . Then, inside of the function yearsUntilRetirement , the other function calculateAge is called, using the value of year as the argument. Since year is the value 1975 , we get age = calculateAge(1975) . Now, within the calculateAge function, the value 1975 is the value corresponding to yearOfBirth . So, running everything through, you get var age = 2016 - 1975 .

If this is too drawn out, I will attempt to clarify further. Drop a comment if you need anything else.