moment

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.5.11/Rx.js"></script>

JavaScript

const h = {label: '2', value: '2'};
const m = {label: '30', value: '30'};
const t = {label: 'PM', value: 'PM'};

const prepareDate = (h, m, t) => {
	return `${h.value}:${m.value}:${t.value}`;
}

const format12h = prepareDate(h, m, t);
console.error(moment(prepareDate(h, m, t), 'hh:mm A').format("HH:mm:ss"));