const str = "😀".repeat(10)

function fold_graphemes(str, state, fun) {
  let arr
  while(null !== (arr = pop_grapheme(str))) {
    state = fun(arr[0], state)
    str = arr[1]
  }
  return state
}

function pop_grapheme(str) {
  if (str === "") return null;
  const segmenter = new Intl.Segmenter();
  const grapheme = segmenter.segment(str)[Symbol.iterator]().next().value.segment;
  return [grapheme, str.slice(grapheme.length)]
}


let sum = 0
for(let i = 0; i < 100000; ++i) {
  sum += fold_graphemes(str, 0, (a, b) => b + a.length)
}
console.log(sum)