JavaScript check if timezone name valid or not

In environments that fully support IANA time zone identifiers in ECMA-402 (ECMAScript Internationalization API), you can try using a time zone in a DateTimeFormat (or in the options of to toLocaleString) and it will throw an exception if it is not a valid time zone. You can use this to test for validity, but only in environments where it is supported.

function isValidTimeZone(tz) {
    if (!Intl || !Intl.DateTimeFormat().resolvedOptions().timeZone) {
        throw new Error('Time zones are not available in this environment');
    }

    try {
        Intl.DateTimeFormat(undefined, {timeZone: tz});
        return true;
    }
    catch (ex) {
        return false;
    }
}

// Usage:
isValidTimeZone('America/Los_Angeles') // true
isValidTimeZone('Foo/Bar') // false

If you cannot be assured of your environment, then the best way would be with moment-timezone

!!moment.tz.zone('America/Los_Angeles') // true
!!moment.tz.zone('Foo/Bar') // false

Of course, you could always extract your own array of time zone names (perhaps with moment.tz.names() and test against that.