I am storing time in a MySQL database as a Unix timestamp and that gets sent to some JavaScript code. How would I get just the time out of it?
For example, in HH/MM/
The modern solution that doesn't need a 40 KB library:
Intl.DateTimeFormat is the non-culturally imperialistic way to format a date/time.
// Setup once
var options = {
    //weekday: 'long',
    //month: 'short',
    //year: 'numeric',
    //day: 'numeric',
    hour: 'numeric',
    minute: 'numeric',
    second: 'numeric'
},
intlDate = new Intl.DateTimeFormat( undefined, options );
// Reusable formatter
var timeStamp = 1412743273;
console.log( intlDate.format( new Date( 1000 * timeStamp ) ) );
                                                                        Use:
var s = new Date(1504095567183).toLocaleDateString("en-US")
console.log(s)
// expected output "8/30/2017"  
and for time:
var s = new Date(1504095567183).toLocaleTimeString("en-US")
console.log(s)
// expected output "3:19:27 PM"
see Date.prototype.toLocaleDateString()
shortest one-liner solution to format seconds as hh:mm:ss: variant:
console.log(new Date(1549312452 * 1000).toISOString().slice(0, 19).replace('T', ' '));
// "2019-02-04 20:34:12"
function getTIMESTAMP() {
  var date = new Date();
  var year = date.getFullYear();
  var month = ("0" + (date.getMonth() + 1)).substr(-2);
  var day = ("0" + date.getDate()).substr(-2);
  var hour = ("0" + date.getHours()).substr(-2);
  var minutes = ("0" + date.getMinutes()).substr(-2);
  var seconds = ("0" + date.getSeconds()).substr(-2);
  return year + "-" + month + "-" + day + " " + hour + ":" + minutes + ":" + seconds;
}
//2016-01-14 02:40:01
                                                                        function timeConverter(UNIX_timestamp){
  var a = new Date(UNIX_timestamp * 1000);
  var months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];
  var year = a.getFullYear();
  var month = months[a.getMonth()];
  var date = a.getDate();
  var hour = a.getHours();
  var min = a.getMinutes();
  var sec = a.getSeconds();
  var time = date + ' ' + month + ' ' + year + ' ' + hour + ':' + min + ':' + sec ;
  return time;
}
console.log(timeConverter(0));
JavaScript works in milliseconds, so you'll first have to convert the UNIX timestamp from seconds to milliseconds.
var date = new Date(UNIX_Timestamp * 1000);
// Manipulate JavaScript Date object here...