dd/mm/yyyy hh:mm:ss

date.js

var d = new Date();
alert(
    ("00" + (d.getMonth() + 1)).slice(-2) + "/" + 
    ("00" + d.getDate()).slice(-2) + "/" + 
    d.getFullYear() + " " + 
    ("00" + d.getHours()).slice(-2) + ":" + 
    ("00" + d.getMinutes()).slice(-2) + ":" + 
    ("00" + d.getSeconds()).slice(-2)
);

duration.js

// https://stackoverflow.com/questions/13903897/javascript-return-number-of-days-hours-minutes-seconds-between-two-dates
console.log(duration('2019-07-17T18:35:25.235Z', '2019-07-20T00:37:28.839Z'));

function duration(t0, t1){
    let d = (new Date(t1)) - (new Date(t0));
    let weekdays     = Math.floor(d/1000/60/60/24/7);
    let days         = Math.floor(d/1000/60/60/24 - weekdays*7);
    let hours        = Math.floor(d/1000/60/60    - weekdays*7*24            - days*24);
    let minutes      = Math.floor(d/1000/60       - weekdays*7*24*60         - days*24*60         - hours*60);
    let seconds      = Math.floor(d/1000          - weekdays*7*24*60*60      - days*24*60*60      - hours*60*60      - minutes*60);
    let milliseconds = Math.floor(d               - weekdays*7*24*60*60*1000 - days*24*60*60*1000 - hours*60*60*1000 - minutes*60*1000 - seconds*1000);
    let t = {};
    ['weekdays', 'days', 'hours', 'minutes', 'seconds', 'milliseconds'].forEach(q=>{ if (eval(q)>0) { t[q] = eval(q); } });
    return t;
}

/*
{
  "days": 2,
  "hours": 6,
  "minutes": 2,
  "seconds": 3,
  "milliseconds": 604
}
*/