CODEWITHSUNDEEP
javascriptarrayssorting
Michael Alexander
Michael Alexander

Reputation: 480

How does this array sorting function actually work?

I was working on some coding challenges for practice and came across one that stumped me. Reading an article about it, I came across the answer, which I cannot understand. The challenge was to create a function that sorts an array of integers in ascending order and returns it. The function is as follows:

function sortAscending(arr) {
    return arr.sort(function(a, b) {
        return a - b;
    });
}

What I can't understand is how sorting using the compare function return a - b actually works. If I have an array of random integers and I take a calculator and apply that arithmetic operation to each, it does not result in an array that is sorted in ascending order, it results in a completely different array. So that tells me I must be completely misunderstanding how this work. Anyone care to explain this to someone with basically no computer science knowledge?

Upvotes: 0

Views: 58

Answers (1)

Paul
Paul

Reputation: 36319

Your compare function (a,b) => a-b is telling the sort function how to sort. In other words, it tells sort how to compare two values at a time. Internally, sort applies your compare function repeatedly until it comes up with the sorted results.

if the return value is less than zero, a should be sorted to an index less than b (so a is placed in the array before b)

If the return value is greater than zero, a should be sorted to an index greater than b.

If the return value IS zero, then the order should remain unchanged.

Any undefined value (in either a or b) gets sorted to the end of the array w/o actually calling the compare function.

This is well documented on MDN

Upvotes: 3

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