Prefix it with a date:

var hms = "01:12:33";
var target = new Date("1970-01-01T" + hms);
console.log(target);

There target.getTime() will give you the number of milliseconds since the start of the day;

Or, if you need it to be today's date:

var now = new Date();
var nowDateTime = now.toISOString();
var nowDate = nowDateTime.split('T')[0];
var hms = '01:12:33';
var target = new Date(nowDate + 'T' + hms);
console.log(target);

There target.getTime() will give you the number of milliseconds since the epoch.

I think it can be a problem about your client or server time config. Check your client's and server's timezone.

Otherwise, you can use this hacky solution (from here)

d = new Date(value) ; d.setTime( d.getTime() - new Date().getTimezoneOffset()*60*1000 );

let unix_timestamp = 1549312452;

// Create a new JavaScript Date object based on the timestamp
// multiplied by 1000 so that the argument is in milliseconds, not seconds
var date = new Date(unix_timestamp * 1000);

// Hours part from the timestamp
var hours = date.getHours();

// Minutes part from the timestamp
var minutes = "0" + date.getMinutes();

// Seconds part from the timestamp
var seconds = "0" + date.getSeconds();

// Will display time in 10:30:23 format
var formattedTime = hours + ':' + minutes.substr(-2) + ':' + seconds.substr(-2);

console.log(formattedTime);

For more information regarding the Date object, please refer to MDN or the ECMAScript 5 specification.

Append 'UTC' to the string before converting it to a date in javascript:

var date = new Date('6/29/2011 4:52:48 PM UTC');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"

Here is the one-liner:

function convertTZ(date, tzString) {
    return new Date((typeof date === "string" ? new Date(date) : date).toLocaleString("en-US", {timeZone: tzString}));   
}

// usage: Asia/Jakarta is GMT+7
convertTZ("2012/04/20 10:10:30 +0000", "Asia/Jakarta") // Tue Apr 20 2012 17:10:30 GMT+0700 (Western Indonesia Time)

// Resulting value is regular Date() object
const convertedDate = convertTZ("2012/04/20 10:10:30 +0000", "Asia/Jakarta") 
convertedDate.getHours(); // 17

// Bonus: You can also put Date object to first arg
const date = new Date()
convertTZ(date, "Asia/Jakarta") // current date-time in jakarta.

   

This is the MDN Reference.

Beware the caveat: function above works by relying on parsing toLocaleString result, which is string of a date formatted in en-US locale , e.g. "4/20/2012, 5:10:30 PM". Each browser may not accept en-US formatted date string to its Date constructor and it may return unexpected result (it may ignore daylight saving).

Currently all modern browser accept this format and calculates daylight saving correctly, it may not work on older browser and/or exotic browser.

side-note: It would be great if modern browser have toLocaleDate function, so we don't have to use this hacky work around.