Use the utc() method of moment to remove the timezone and display everything in universal time.

moment.utc('2015-01-22T16:11:36.36-07:00').format('l LT')

That will display the time as it is in UTC without any timezone offset. If you want to display the time as it was recorded in the user/server timezone you can parse the zone information when you construct a moment instance and have it use the timezone recorded in the parsed string.

moment.parseZone('2015-01-22T16:11:36.36-07:00').format('l LT');

With either of these approaches you should consider labeling the time in some way to reflect the timezone the time corresponds to. Failing to do this could lead to a lot of confusion for the end users.

You can do this with moment.js using moment.utc().

http://momentjs.com/docs/#/parsing/utc/

moment([2011, 10, 8, 5]).format(); // different output based on timezone
moment.utc([2011, 10, 8, 5]).format(); // same output for all timezones

The way moment.utc works is by setting a flag internally to use getUTCMinutes instead of getMinutes, thus the output is the same in all timezones.

Have you tried parseZone?

moment.parseZone(end).format('MM/DD/YYYY');

That should keep your UTC offset applied. You can then also calculate the UTC offset, if you wanted to save that:

moment.parseZone(end).format('MM/DD/YYYY').utcOffset();

To meet the requirement you described (keeping the local time while changing the offset) you can do the following:

var result = moment.parseZone("2019-11-19T07:05:00+01:00").utcOffset(0, true).format();
console.log(result); //=> "2019-11-19T07:05:00Z"

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.min.js"></script>

Step by step explained:

moment.parseZone("2019-11-19T07:05:00+01:00") // Parses the string, retaining the offset provided
      .utcOffset(0, true)  // sets the offset to zero while keeping the local time
      .format()            // formats the output, using Z to represent UTC

However - You should recognize that these are not the same moments in time. The output timestamp is one hour earlier than the input timestamp. This is explained in the documentation as follows (emphasis mine):

The utcOffset function has an optional second parameter which accepts a boolean value indicating whether to keep the existing time of day.

• Passing false (the default) will keep the same instant in Universal Time, but the local time will change.

• Passing true will keep the same local time, but at the expense of choosing a different point in Universal Time.

Thus, it is usually the wrong choice when you already have a specific point in time, either in UTC or as an offset from UTC (like your example input value).

Instead, you should expect that converting from local time to UTC will indeed change the date and time portion of the timestamp. You can use .utcOffset(0, false), or .utcOffset(0), or simply .utc() to do the conversion correctly.

utcOffset is what you need:

var date1 = '2018-12-21T15:58:39.35-05:00'
var m = moment(date1).utcOffset(date1);
var fmtDate = m.format('YYYY-MM-DD hh:mm a');

$('#output').append(fmtDate); // result is as you expected: 2018-12-21 03:58 pm

here is the example: https://jsfiddle.net/73pa1qkz/9/

As pointed out in Manto's answer, .utcOffset() is the preferred method as of Moment 2.9.0. This function uses the real offset from UTC, not the reverse offset (e.g., -240 for New York during DST). Offset strings like "+0400" work the same as before:

// always "2013-05-23 00:55"
moment(1369266934311).utcOffset(60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).utcOffset('+0100').format('YYYY-MM-DD HH:mm')

The older .zone() as a setter was deprecated in Moment.js 2.9.0. It accepted a string containing a timezone identifier (e.g., "-0400" or "-04:00" for -4 hours) or a number representing minutes behind UTC (e.g., 240 for New York during DST).

// always "2013-05-23 00:55"
moment(1369266934311).zone(-60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).zone('+0100').format('YYYY-MM-DD HH:mm')

To work with named timezones instead of numeric offsets, include Moment Timezone and use .tz() instead:

// determines the correct offset for America/Phoenix at the given moment
// always "2013-05-22 16:55"
moment(1369266934311).tz('America/Phoenix').format('YYYY-MM-DD HH:mm')

See moment issue #887, directly regarding this. It may be easier in a future version, but the current workaround is as follows:

var input = "2013-09-20 23:59:59 +0100";
var m = moment(input).zone(input);
m.format("DD-MM-YYYY HH:mm:ss ZZ")