JavaScript: add a day to a date if one time is less than another

addDay.js

const startedTime = '14:30';
const completedTime = '01:15';
const startedDate = '20/01/2019';

if (completedTime < startedTime) {

    const [day, month, year] = startedDate.split('/');
    const currentDate = new Date(Date.parse(`${year}-${month}-${day}`));
    const currentDateUnix = currentDate.valueOf();
    const newDateUnix = currentDateUnix + 24*60*60*1000;
    const newDate = new Date(newDateUnix);

    const newDay = ("0" + newDate.getDate()).slice(-2);
    const newMonth = ("0" + (newDate.getMonth() + 1)).slice(-2);
    completedDate = `${newDay}/${newMonth}/${newDate.getFullYear()}`;

    console.log(completedDate);

}