我的updateState函数中的参数来自哪里？

Question

I'm just starting JS and React using the fullstack.io book.

In the book, there is a section of code:

updateState: function () {
    const products = Data.sort((a, b) => {
        return b.votes - a.votes;
}

Now everytime the updateState function is called in the code samples, there are no parameters passed in... so how would the "a" & "b" parameters used in the Data.sort be populated?

Thank you.

Answer 1

I'm not sure what Data is but let's assume it's an array.

Array.prototype.sort is a function that takes a comparator callback function (a, b) => { ... } .
The function compares elements a and b .
If the function returns a number less than 0, a comes before b (ascending order).
Otherwise b comes before a (descending order).

The key takeaway is that a and b are passed by sort under the hood. You only need to worry about providing the callback which determines the sort order.

For example:

let arr = [2, 4, 7, 1]

arr.sort((a, b) => a - b) // => [1, 2, 4, 7]

arr.sort((a, b) => b - a) // => [7, 4, 2, 1]