currencyConverter.js

const DEFAULT_CURRENCY = 'EUR';
const baseURL = 'http://data.fixer.io/api';
const accessToken = 'xxxxxxx';

const currencySymbols = ['USD', 'EUR', 'JPY'];

const symbolsAPIUrl = `${baseURL}/latest?access_key=${accessToken}&symbols=${currencySymbols.join(',')}&format=1`;

const sourceInput = document.getElementById('source');
const targetInput = document.getElementById('target');
const sourceSelect = document.getElementById('source-select');
const targetSelect = document.getElementById('target-select');

let apiCurrencyRates = {};
let baseCurrencyRates = {}

async function initDataSource() {
    console.log('initializing data sources...');
    try {
        const response = await axios.get(symbolsAPIUrl);
        console.log('the response', response);
        return response.data;
    } catch (e) {
        console.log('the err', e)
    }
}

window.onload = async () => {
    const data = await initDataSource();
    apiCurrencyRates = data.rates;
    setCurrencyAsBase(DEFAULT_CURRENCY);
    console.log('the reates', baseCurrencyRates);

    // setup event listeners for input changes
    sourceInput.addEventListener('input', handleSourceChange);
    targetInput.addEventListener('input', handleTargetChange);
    
    // setup event listeners for dropdown changes
    sourceSelect.addEventListener('change', handleSourceCurrencyChange);
    targetSelect.addEventListener('change', handleTargetCurrencyChange);
    
}

function handleSourceChange(e) {
    const convertedValue = Number((baseCurrencyRates[targetSelect.value] * e.target.value).toFixed(2));
    targetInput.value = convertedValue;
}


function handleTargetChange(e) {
    const convertedValue = Number((e.target.value / baseCurrencyRates[targetSelect.value]).toFixed(2));
    sourceInput.value = convertedValue;
}

function handleSourceCurrencyChange() {
    setCurrencyAsBase(sourceSelect.value);
    handleSourceChange({target: {value: sourceInput.value}})
}

function handleTargetCurrencyChange() {
    setCurrencyAsBase(targetSelect.value);
    handleTargetChange({target: {value: targetInput.value}})
}

function setCurrencyAsBase(currency) {
    const currencyValue = apiCurrencyRates[currency];
    
    for (const [curr, value] of Object.entries(apiCurrencyRates)) {
        baseCurrencyRates[curr] = value / currencyValue;
    }
    
    console.log('new base', baseCurrencyRates);
}