npm install js-joda
npm install js-joda-timezone

const jsJoda = require('js-joda')
    .use(require('js-joda-timezone'))

const { LocalDateTime, ZoneId, ZonedDateTime } = jsJoda;
     
LocalDateTime
    .parse('2016-06-30T11:30')
    .atZone(ZoneId.of('Europe/Berlin'))
    .toString()  // 2016-06-30T11:30+02:00[Europe/Berlin]
     
ZonedDateTime
    .parse('2016-06-30T11:30+02:00[Europe/Berlin]') 
    .withZoneSameInstant(ZoneId.of('America/New_York'))
    .toString() // 2016-06-30T05:30-04:00[America/New_York]

ZonedDateTime
    .parse('2016-06-30T11:30+02:00[Europe/Berlin]')
    .withZoneSameLocal(ZoneId.of('America/New_York'))
    .toString() // 2016-06-30T11:30-04:00[America/New_York]

import { use as jsJodaUse, ZonedDateTime, ZoneId } from 'js-joda'
import jsJodaTimeZone from 'js-joda-timezone'

jsJodaUse(jsJodaTimeZone)

const zdt = ZonedDateTime.now(ZoneId.of('America/New_York'))

<script src="../dist/js-joda.js"></script>
<script src="../dist/js-joda-timezone.js"></script>
<script>
    // use js-joda-timezone
    JSJoda.use(JSJodaTimezone)

    // copy all js-joda classes to the global scope
    for(let key in JSJoda) { this[key] = JSJoda[key]; }
        
    LocalDateTime
        .parse('2016-06-30T11:30')
        .atZone(ZoneId.of('Europe/Berlin'))
        .toString()  // 2016-06-30T11:30+02:00[Europe/Berlin]
         
    ZonedDateTime
        .parse('2016-06-30T11:30+02:00[Europe/Berlin]') 
        .withZoneSameInstant(ZoneId.of('America/New_York'))
        .toString() // 2016-06-30T05:30-04:00[America/New_York]

    ZonedDateTime
        .parse('2016-06-30T11:30+02:00[Europe/Berlin]')
        .withZoneSameLocal(ZoneId.of('America/New_York'))
        .toString() // 2016-06-30T11:30-04:00[America/New_York]
</script>