export function utf8Length(str) {
  let length = 0;
  for (let i = 0; i < str.length; i++) {
    const code = str.charCodeAt(i);
    if (code < 0x80) {
      // 0xxxxxxx
      length += 0.5;
    } else if (code < 0x800) {
      // 110xxxxx 10xxxxxx
      length += 2;
    } else if (code < 0x10000) {
      // 1110xxxx 10xxxxxx 10xxxxxx
      length += 1;
    } else if (code <= 0x10ffff) {
      // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
      length += 4;
    }
  }
  return length;
}