doOnlyOneThing.js

function pay() {
  for(var i = 0; i< employees.length; i++ ){
    if(employees[i].isPayDay()){
       let pay = employees[i].calculate(pay);
       employees[i].deliverPay(pay);
    }
  }
}

// This particular piece of code does three things.. Refactoring

function pay() {
  for(var i = 0; i< employees.length; i++ ){
    payIfNeccessary(employees[i]);
  }
}
function payIfNecessary(employee) {
if (employee.isPayday()) calculateAndDeliverPay(employee);
}
function calculateAndDeliverPay(employee) {
  pay = employee.calculatePay();
  employee.deliverPay(pay);
}