JavaScript .sort() undefined value always should be "earlier"

Question

I want to sort an array of objects by multiple fields (3-4 in my case). Some values of object could be undefined and those values must be always "earlier" in sorting (ascending and descending). In my case everything works when sorting is descending, but in case of ascending values which are undefined are always in the bottom. Type of those values is always a string and I could call only .sort() method nothing before it and after. My code looks like this:

[{id: "1", label: "Z", code: "Z"}, 
 {id: "1", code: "A"},
 {id: "2", label: "A",},
 {id: "3", label: "A", code: "A"}]
     .sort((a,b) => {
          return a.id.localeCompare(b.id)
             || a.label.localeCompare(b.label)
             || a.code.localeCompare(b.code)
     );

If you want to check if a property exists in JS, the see: https://stackoverflow.com/a/136411/4688321 — kiner_shah, Feb 06 '23 at 08:08
Based on what do you want to sort? What is the exact use case? — kiner_shah, Feb 06 '23 at 08:09
So what's the expected order for your example. The simplest would probably be, checking for `undefined` before using `localeCompare` — derpirscher, Feb 06 '23 at 08:09

score 1 · Accepted Answer · answered Feb 06 '23 at 08:34

Just write your own comparison function. 0 means they're the same, a positive number means b should come first, a negative number means a should come first.

const localeCompareUndefined = (a, b, locales, options) => {
  if (a === undefined && b === undefined) return 0;
  else if (b === undefined) return 1;
  else if (a === undefined) return -1;
  else return a.localeCompare(b, locales, options);
}

const data = [{id: "1", label: "Z", code: "Z"}, 
 {id: "1", code: "A"},
 {id: "2", label: "A",},
 {id: "3", label: "A", code: "A"}]
.sort((a, b) => {
  return localeCompareUndefined(a.id, b.id) ||
    localeCompareUndefined(a.label, b.label) ||
    localeCompareUndefined(a.code, b.code)
});

console.log(data);

JavaScript .sort() undefined value always should be "earlier"

1 Answers1