script.ts

interface Payroll {
    empNo: string;
    vacationDays: number;
}

interface AddressBook {
    empNo: string;
    email: string;
}

interface WorkHistory {
    empNo: string;
    name: string;
    yearsEmployed: number;
}

interface EmailApi {
    sendEmail(email: string, body: string);
}

function NewEmailVacationGrant(
    emailApi: EmailApi,
    histories: WorkHistory[],
    addresses: AddressBook[],
    payroll: Payroll[]
) {
    // Assumption:
    // - histories.length == addresses.length == payroll.length

    // create hash maps for addresses and payroll; this removes the need to
    // use the slow, linear Array.find() method
    var mappedAddresses:AddressBook[] = [];
    for (var i:number = 0; i < addresses.length; i++) {
        mappedAddresses[addresses[i].empNo] = Object.assign({}, addresses[i]);
    }

    var mappedPayroll:Payroll[] = [];
    for (var i:number = 0; i < payroll.length; i++) {
        mappedPayroll[payroll[i].empNo] = Object.assign({}, payroll[i]);
    }

    for (var i:number = 0; i < histories.length; i++) {
        var employee:WorkHistory = histories[i];
        var address:AddressBook = mappedAddresses[employee.empNo];

        var newVacationBalance:number = employee.yearsEmployed + mappedPayroll[employee.empNo].vacationDays;

        emailApi.sendEmail(
            address.email,
            `Dear ${employee.name},\n` +
            `Based on your ${employee.yearsEmployed} years of employment, you have been granted ${employee.yearsEmployed} bonus days of vacation, bringing your total to ${newVacationBalance}.`
        );
    }
}

function OldEmailVacationGrant(
    emailApi: EmailApi,
    histories: WorkHistory[],
    addresses: AddressBook[],
    payroll: Payroll[]
) {
    for (var i:number = 0; i < histories.length; i++) {
        let employee = histories[i];
        let address = addresses.find(x => x.empNo==employee.empNo);
        let employeePayroll = payroll.find(x => x.empNo==employee.empNo);

        let newVacationBalance = employee.yearsEmployed + employeePayroll.vacationDays;

        emailApi.sendEmail(
            address.email,
            `Dear ${employee.name}\n` +
            `based on your ${employee.yearsEmployed} years of employment, you have been granted ${employee.yearsEmployed} days of vacation, bringing your total to ${newVacationBalance}`
        );
    }
}

(function CompareOldVSNew() {
    // generate dummy data for testing
    var payroll:Payroll[] = [];
    var addressBook:AddressBook[] = [];
    var workHistory:WorkHistory[] = [];

    for (var i:number = 0; i < 10000; i++) {
        var empNo:string = Math.floor((Math.random() * 10000000)).toString();

        payroll.push({
            empNo: empNo,
            vacationDays: 10 // default starting point
        });

        addressBook.push({
            empNo: empNo,
            email: 'foo@' + empNo + '.com'
        });

        workHistory.push({
            empNo: empNo,
            name: 'Bar ' + empNo,
            yearsEmployed: Math.floor(Math.random() * 15) + 1 // 1-15 years
        });
    }

    // dummy EmailClient
    class EmailClient {
        sendEmail(email: string, body: string):void {
            // console.log("Sending email to: " + email + ".\n");
            // console.log(body + "\n");
        }
    }
    var emailClient:EmailApi = new EmailClient();

    var newAverage:number = 0;
    var oldAverage:number = 0;
    var sampleRuns:number = 10;

    for (var i:number = 0; i < sampleRuns; i++) {
        const newStart:number = Date.now();
        NewEmailVacationGrant(emailClient, workHistory, addressBook, payroll);
        newAverage += Date.now() - newStart;

        const oldStart:number = Date.now();
        OldEmailVacationGrant(emailClient, workHistory, addressBook, payroll);
        oldAverage += Date.now() - oldStart;
    }

    console.log('Average runtime of new implementation: ' + (newAverage / sampleRuns).toString() + 'ms.');
    console.log('Average runtime of old implementation: ' + (oldAverage / sampleRuns).toString() + 'ms.');
})();