Upper case letters first when sorting with localeCompare()

Question

I want to sort an array with strings alphabetically. However, upper case letters should be always before the corresponding lower case letter (example order: A a B b ...).

To archive this, I have tried to use localCompare with caseFirst: "upper" and sensitivity: "case":

const input = ["ADR 2023", "Added Values", "DEMO build", "DEMO Build", "2nd Outlook", "demo award"]
const output = input.sort((a, b) => a.localeCompare(b, "en-US", { caseFirst: "upper", sensitivity: "case" }))
console.log(output)

I would expect the output to be:

["2nd Outlook", "ADR 2023", "Added Values", "DEMO Build", "DEMO build", "demo award"]

Unfortunately, the output is:

["2nd Outlook", "Added Values", "ADR 2023", "demo award", "DEMO Build", "DEMO build"]

How can I get the expected order? In the example, I have used en-US as locale. However, in my real project, it can be any supported locale with a length of five characters.

Answer 1

1. Don't use localeCompare() since it creates Intl.Collator every time - tooooo slow.
2. You can compare char by char ensuring that any number of upper case letters could be processed.

const input = ["ADR 2023", "Added Values", "DEMO build", "DEMO Build", "2nd Outlook", "demo award"];
const {compare} = Intl.Collator("en-US", { caseFirst: "upper"});
const output = input.sort((a, b) => {
  for(let i = 0; i < a.length && i < b.length; i++){
    const r = compare(a[i], b[i]);
    if(r) return r;
  }
  if(a.length > b.length) return 1;
  if(a.length < b.length) return -1;
  return 0;
})
console.log(output)

A string iterator version as suggested by VLAZ:

const input = ["ADR 2023", "Added Values", "DEMO build", "DEMO Build", "2nd Outlook", "demo award"];
const {compare} = Intl.Collator("en-US", { caseFirst: "upper"});
const output = input.sort((a, b) => {
  const ia = a[Symbol.iterator](), ib = b[Symbol.iterator]();
  while(true){
    const ca = ia.next().value, cb = ib.next().value;
    if(!ca) return ba ? -1 : 0
    if(ca && !cb) return 1;
    const r = compare(ca, cb);
    if(r) return r;
  }
})
console.log(output)