Conversor_moneda/script.js

async function api(base){
	const res = await fetch(`https://api.exchangeratesapi.io/latest?base=${base}`);
	const data = await res.json();
	return data.rates;
}

async function convert(){
	const base = document.getElementById('curr').value;
	const rates = await api(base);
	const cur = document.getElementById('curr2').value;
	var coef = rates[cur];
	if (base==cur){
		coef = 1;
	}
	var val = document.getElementById('val').value;
	document.getElementById('res').textContent = Number((val*coef).toFixed(2)).toLocaleString('en') + ' ' +document.getElementById('curr2').value;
}

async function convert2(){
	const base = document.getElementById('rev').value;
	const rates = await api(base);
	const cur = document.getElementById('rev2').value;
	var coef = rates[cur];
	if (base==cur){
		coef = 1;
	}
	var val = document.getElementById('val2').value;
	document.getElementById('res2').textContent = Number((val*coef).toFixed(2)).toLocaleString('en') + ' ' +document.getElementById('rev2').value;
}

const from1 = document.getElementById('curr');
const to1 = document.getElementById('curr2');

const from2 = document.getElementById('rev');
const to2 = document.getElementById('rev2');

from1.onchange = function(a){
	to2.value = a.target.value;
};

to1.onchange = function(a){
	from2.value = a.target.value;
};

from2.onchange = function(a){
	to1.value = a.target.value;
};

to2.onchange = function(a){
	from1.value = a.target.value;
};