map_example.js

const TOTAL_WORKING_DAYS = 261;

const getDailyRate = salary => Math.floor(((salary * 12) / (TOTAL_WORKING_DAYS)));

const dailyRate = employee => Object.assign({}, { employee: employee.employee, dailyRate: getDailyRate(employee.salary) });

//Returns a new set of empoloyees with dailyRate and name
const newEmployees = employees.map(dailyRate);

//new data
console.log(newEmployees);

//old data
console.log(employees);