/**
 * Example 2:
 * Calculating average salary gain per year. callbackFn is our core
 * function to dectate gow to handle the data.
 */
function callbackFn([tSal, tExp], data) {
    tSal = tSal + data.salary;
    tExp = tExp + data.expInYears;
    return [tSal, tExp];
}

// using destructuring to extract the final result from myReducer
const [ tSalary, tExperince ] = myReducer(developers, callbackFn, [0,0]);
const aveSalPerYear = Math.floor(tSalary/tExperince);

console.log(aveSalPerYear); // 25833