let_and_const.js

'use strict'
const _loadDataForUser = (url, callback) => {
  setTimeout(callback, 2 * 1000)
}
const loadDataForUsers = (userNames) => {
  for (let i in userNames) {
    _loadDataForUser(`users/${userNames[i]}`, function () {
      console.log('Fetching for ', userNames[i])
    })
  }
}

loadDataForUsers(['John', 'Eve', 'Oleg'])
// Fetching for  John
// Fetching for  Eve
// Fetching for  Oleg

const COUNT = 4
// const COUNT = 2 raise SyntaxError: Identifier 'COUNT' has already been declared