let locale = 'pt-BR';
let options = { minimumFractionDigits: 0, maximumFractionDigits: 2 };
let formatador = new Intl.NumberFormat(locale, options);
[ 987654.321, 987654321 ].forEach(n => {
formatador.format(n);
});
[ 987654.321, 987654321 ].forEach(n => {
n.toLocaleString(locale, options);
});