 # FAQ: Code Challenges: Intermediate JavaScript - sortYears()

This community-built FAQ covers the “sortYears()” exercise from the lesson “Code Challenges: Intermediate JavaScript”.

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const sortYears = arr => arr.sort((x, y) => y - x)

I don’t understand what " (x, y) => y - x " is doing, why would it return a year and not the value of y minus x?

1 Like

I want to know that too, I don’t understand that… Can some one explain how does it work?

because of how sort works, here is useful documentation:

we pass our own function to the sort method to determine sorting order. The result of `y - x` is then used to determine were the element should be sorted. for example, the first two elements in our array are:

``````1970, 1999
``````

so if we then fill in our function which determine sorting order:

``````(1970, 1999) => 1999 - 1970
``````

which gives a a value higher then 0, which means `y` comes before `x`.

in short, the `.sort()` method will call your function to determine sorting order.