const str = "hello world! this is jsbench. café résumé";

function capitalizeFirst_charAt(str) {
  return str && str.charAt(0).toUpperCase() + str.slice(1);
}

function capitalizeFirst_replaceStart(str) {
  return str && str.replace(/^./, c => c.toUpperCase());
}

function capitalizeFirst_index(str) {
  return str && str[0].toUpperCase() + str.slice(1);
}

String.prototype.capitalizeFirst_prototype = function () {
  return this.charAt(0).toUpperCase() + this.slice(1);
};

function capitalizeFirstLetter(s) {
  return s && s[0].toUpperCase() + s.slice(1);
}

function capitalizeWords_unicode(str) {
  if (!str) return str;
  return str.replace(/(^|[^\p{L}\p{N}_])(\p{L}\p{M}*)/gu, (_, pre, word) => pre + capitalizeFirstLetter(word));
}