hyperskill project Simple Currency Converter (Frontend path)

main.js

const readline = require('readline');
const ROUND_TO_DIGITS = 4;
const COMMAND_CONVERT = 1;
const COMMAND_EXIT = 2;

const GREETING = 'Welcome to Currency Converter!';

const rates = getRates();

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});

function getRates() {
    return new Map([
        ['USD', 1.0],
        ['JPY', 113.5],
        ['EUR', 0.89],
        ['RUB', 74.36],
        ['GBP', 0.75]
    ]);
}

function printMap() {
    rates
        .forEach((k, v) => console.log(`1 USD equals  ${k} ${v}`));
}

function readCurrency(label) {
    return new Promise((resolve => {
        rl.question(`${label}:`, (answer) => {
            if (!rates.has(answer.toUpperCase())) {
                console.log('Unknown currency');
                process.exit(1)
            }
            resolve(answer.toUpperCase());
        });

    }))
}

function readAmount() {
    return new Promise((resolve => {
        rl.question("Amount:", (answer) => {
            const num = Number(answer);
            if (isNaN(num) || num < 1) {
                console.log("The amount can not be less than 1");
                process.exit(1)
            }
            resolve(num);
        });
    }))
}

async function readCommand() {
    console.log(`What do you want to do?
1-Convert currencies 2-Exit program`);
    return new Promise((resolve => {
        rl.question("", (answer) => {
            resolve(Number(answer));
        });
    }))
}

async function askData() {
    while (true) {
        const command = await readCommand();

        if (!command || (command !== COMMAND_CONVERT && command !== COMMAND_EXIT)) {
            console.log("Unknown input");
            continue;
        }

        if (command === COMMAND_CONVERT) {
            const from = await readCurrency("From");
            const to = await readCurrency("To");
            const amount = await readAmount();

            const k = ((1 / rates.get(from)) * rates.get(to));
            const result = (amount * k)
                .toFixed(ROUND_TO_DIGITS);
            console.log(`Result: ${amount} ${from} equals ${result} ${to}`)
        } else {
            process.exit(0)
        }
    }
}


function main() {
    console.log(GREETING);
    printMap();
    askData();
}

main();