Отсортируйте список по свойству и добавьте объект перед изменением каждой первой буквы в JavaScript

let data = [{
  name: 'Julia'
}, {
  name: 'Ismeh'
}, {
  name: 'Alison'
}, {
  name: 'Andrea'
}, {
  name: 'Betty'
}];

let combined = data.reduce((result, item) => {
  let letter = item.name[0].toUpperCase();
  if (!result[letter]) {
    result[letter] = [];
  }

  result[letter].push(item);
  return result;
}, {});

console.info(combined);

// Iterate over the result
Object.keys(combined).forEach(key => {
  // key will be the first letter of the user names and
  // combined[key] will be an array of user objects
  console.info(key, combined[key]);
});

const unsortedPeople = [{name: 'Julia'}, {name: 'Ismeh'}, {name: 'Alison'}, {name: 'Andrea'}, {name: 'Betty'}];
const sortedUsers = unsortedPeople.sort((a, b) => a.name.localeCompare(b.name))
const final = sortedUsers.reduce((finalSoFar, user) => {
  const thisUserFirstChar = user.name[0];
  if (finalSoFar.length === 0) addHeader();
  else {
    const lastUserFirstChar = finalSoFar[finalSoFar.length - 1].name[0];
    if (lastUserFirstChar !== thisUserFirstChar) addHeader();
  }
  finalSoFar.push(user);
  return finalSoFar;
  function addHeader() {
    finalSoFar.push({ header: thisUserFirstChar });
  }
}, []);

console.info(final);

var users = [{name: 'Julia'}, {name: 'Ismeh'}, {name: 'Alison'}, {name: 'Andrea'}, {name: 'Betty'}]

const sortedUsers = users.sort((a, b) => a.name.localeCompare(b.name))
var currentHeader 
let final = sortedUsers.reduce((a, user) => {
    if (currentHeader !==  user.name[0]) {
        currentHeader = user.name[0]
        a.push({header: currentHeader})
    }
    a.push(user)
    return a
},[])

console.info(final)

const users = [{name: 'Julia'}, {name: 'Ismeh'}, {name: 'Alison'}, {name: 'Andrea'}, {name: 'Betty'}];

let lastIndex;
let result = [];
users.sort((a, b) => {
  return a.name > b.name;
}).forEach((user) => {
  const index = user.name.charAt(0);
  if (index !== lastIndex) {
    result.push({
      header: index
    });
  }
  lastIndex = index;
  result.push(user.name);
}, []);






console.info(result);