Евгений Фролов

const input = document.querySelector(".your input classname")
input.addEventListener('change', (event) => {
    console.log(event.target.checked)
})

const employees = {
    frontend: 12000,
    backend: 10000,
    designer: 8000,
};

const total = (employees = {}) =>
    Object.values(employees).reduce((salary, employeeSalary) => salary + employeeSalary, 0);

console.log(total(employees))
employees.manager = 5000;
console.log(total(employees))

const employeesList = ['frontend', 'backend', "designer"];
const salaries = {
    frontend: 12000,
    backend: 10000,
    designer: 8000,
    total: (staff = []) => staff.reduce((salary, employeeSalary) => salary + employeeSalary, 0),
    dayPay() {
        alert('We mush pay salary on Tuesday!');
    },
};

salaries.total(employeesList) // 30000
employees.manager = 5000;
employeesList.push('manager');
salaries.total(employeesList) // 35000