如何将点分隔字符串中的第一个单词大写？

function capitalizeFirstWord(str) {
  var words = str.split('.');
  var firstWord = words[0];
  var capitalizedFirstWord = firstWord.charAt(0).toUpperCase() + firstWord.slice(1);
  var result = capitalizedFirstWord + str.slice(firstWord.length);
  return result;
}

var input = "hello.world.how.are.you";
var output = capitalizeFirstWord(input);
console.log(output);