const str = "😀".repeat(10)

const segmenter = new Intl.Segmenter();
function fold_graphemes(str, state, fun) {
  for (const { segment: grapheme } of segmenter.segment(str)) {
    state = fun(grapheme, state)
  }
  return state
}

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