<h2></h2>
<div>Last: <span></span></div>

const elTitle = document.querySelector('h2');
const elText = document.querySelector('div > span');

const PAIR = 'BTC/USDT';

const exchange = new ccxt.binance ();
const update = async () => {
  const { last } = await exchange.fetchTicker(PAIR);
  elTitle.innerText = PAIR;
  elText.innerText = last;
  
  setTimeout(update, 5000);
};

update();