JavaScript group by and count function

I use this function in JavaScript:

function groupByAndCount(data, ...keys) {
  const {
    length
  } = keys;
  return Object.values(data[keys[0]].reduce((acc, _, i) => {
    const group = keys.map(key => data[key][i]);
    (acc[JSON.stringify(group)] ??= [...group, 0])[length]++;
    return acc;
  }, {}));
}

const data = {
  type: ["a", "a", "b", "c", "d", "a", "a", "b"],
  program: ["P1", "P1", "P2", "P1", "P2", "P2", "P2", "P1"],
  reference: ["ref1", "ref2", "ref3", "ref4", "ref5", "ref6", "ref7", "ref8"]
}

const result = groupByAndCount(data, "program", "type");
console.log(result);

It worked fine until today but now I get this error:

ERROR: Unexpected token (5:38)

MEDevel.com: Open-source for Healthcare and Education

Collecting and validating open-source software for healthcare, education, enterprise, development, medical imaging, medical records, and digital pathology.

Visit Medevel

Do you know how to solve this? I don’t understand it
I just understand that the "5" in "(5:38)" corresponds to the line 5:

(acc[JSON.stringify(group)] ??= [...group, 0])[length]++;

>Solution :

The "ERROR: Unexpected token (5:38)" is referencing the Nullish coalescing assignment (??=) operator. The error suddenly popping up could be due to running the code in a different environment.

This operator only assigns a value to a operand if that operand is null or undefined.

Try replacing the logic. It will look less beautiful but should work again.

if (!acc[JSON.stringify(group)]) {
    acc[JSON.stringify(group)] = [...group, 0];
}
acc[JSON.stringify(group)][length]++;

I have not tested it myself but it should work.