CODEWITHSUNDEEP
javascript
johnDoe
johnDoe

Reputation: 795

Sorting an array with a compare function - javascript

I came across this sorting of an array and I do not understand the compare function at the point where '-1 : 1' is included. Please can some one explain to me what the compare function is doing exactly?

const rows = [
  createECG('ad0917d4-e02d-4c46-a5aa-dd83717684e9', '28/06/2022', 'pending'),
  createECG('9034124a-2ac8-4d52-8711-ef1351a5c18a', '18/05/2022', 'complete'),
  createECG('a2a7a1f4-81a0-4b70-b1e2-ee7a384a1f4f', '01/05/2022', 'pending'),
  createECG('e5427e62-5897-4eee-a6a6-8f9925feef96', '21/04/2022', 'complete')
].sort((a) => (a.status === 'pending' ? -1 : 1)); // The object 'a' has a property called 'status'

console.log(rows);

function createECG(id, date, status) {
  return {id, date, status};
}

Upvotes: 0

Views: 141

Answers (3)

Hans Murangaza DRCongo
Hans Murangaza DRCongo

Reputation: 860

Sorting is just like filtering, your code means... When a.status === 'pending' equal to 1, means this item has the status property set to pending, and when it equals -1 means the status is not set to pending, then as 1 is correct and superior then Items with pending status will come first

Upvotes: 1

Barmar
Barmar

Reputation: 781769

The comparison function returns -1 if the first argument a as lower than b if its status is pending. This indicates that a is lower than b, so it should be sorted ahead. The intended result is that all the pending elements will be at the front of the result.

But this isn't really valid, because the comparison function is required to be consistent -- if a is lower than b, then b should not also be lower than a. When it's comparing two pending objects, it will return -1 when they're passed in either order. The comparison function should return 0 in this case, but it doesn't.

Upvotes: 2

Nina Scholz
Nina Scholz

Reputation: 386700

You need to take the delta of the comparison for a symmetrically sorting.

function createECG(id, date, status) {
    return { id, date, status };
}

const
    rows = [
        createECG('ad0917d4-e02d-4c46-a5aa-dd83717684e9', '28/06/2022', 'pending'),
        createECG('9034124a-2ac8-4d52-8711-ef1351a5c18a', '18/05/2022', 'complete'),
        createECG('a2a7a1f4-81a0-4b70-b1e2-ee7a384a1f4f', '01/05/2022', 'pending'),
        createECG('e5427e62-5897-4eee-a6a6-8f9925feef96', '21/04/2022', 'complete')
    ]
    .sort((a, b) => (b.status === 'pending') - (a.status === 'pending'));

console.log(rows);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Upvotes: 1

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