.format('z') doesn't work for 0.5.13 if other dependency uses 0.5.25

[marneborn]

We are currently using moment-timezone@0.5.13 but we have a dependency on 0.5.25.
The two do not play nicely together.

The .format('z') gives "UTC" when using the @0.5.13 version after the 0.5.25 version has been required. Anything <=0.5.23 seems to have this problem.

To reproduce

mkdir moment-tz-problem
cd moment-tz-problem
npm init --force
yarn add moment-timezone@0.5.13
yarn add ical-generator@1.7.1

$ node -e "const moment = require('moment-timezone'); console.log(moment().tz('US/Eastern').format('z'));"
EDT
$ node -e "require('ical-generator'); const moment = require('moment-timezone'); console.log(moment().tz('US/Eastern').format('z'));"
UTC

yarn list v1.9.4
├─ ical-generator@1.7.1
│  ├─ moment-timezone@^0.5.25
│  └─ moment-timezone@0.5.25
│     └─ moment@>= 2.9.0
├─ moment-timezone@0.5.13
│  └─ moment@>= 2.9.0
└─ moment@2.24.0

The yarn.lock

# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
# yarn lockfile v1


ical-generator@1.7.1:
  version "1.7.1"
  resolved "https://registry.yarnpkg.com/ical-generator/-/ical-generator-1.7.1.tgz#8f994a44d2bb9da7b0f941723557fa6dbbf7c5a8"
  dependencies:
    moment-timezone "^0.5.25"

moment-timezone@0.5.13:
  version "0.5.13"
  resolved "https://registry.yarnpkg.com/moment-timezone/-/moment-timezone-0.5.13.tgz#99ce5c7d827262eb0f1f702044177f60745d7b90"
  dependencies:
    moment ">= 2.9.0"

moment-timezone@^0.5.25:
  version "0.5.25"
  resolved "https://registry.yarnpkg.com/moment-timezone/-/moment-timezone-0.5.25.tgz#a11bfa2f74e088327f2cd4c08b3e7bdf55957810"
  dependencies:
    moment ">= 2.9.0"

"moment@>= 2.9.0":
  version "2.24.0"
  resolved "https://registry.yarnpkg.com/moment/-/moment-2.24.0.tgz#0d055d53f5052aa653c9f6eb68bb5d12bf5c2b5b"

[naz]

Have found a similar issue when running in Node environment. The problem started from version 0.5.24 and the formatting for dates has now changed. For example, when having moment-timezone @ 0.5.23, the following works:

moment(new Date('2013-10-18T23:58:44.000Z')).format()
-> "2013-10-18T23:58:44Z"

when bumping the version to 0.5.24 the output is:

moment(new Date('2013-10-18T23:58:44.000Z')).format()
"2013-10-19T01:58:44+02:00"

The change, I suspect, that has affected the behavior is this commit - 6b7b558

I wasn't successful to reproduce it in a clean environment though (without other dependencies), but it has happened in Ghost core code after merging this version bump - TryGhost/Ghost#10837, build that failed is https://travis-ci.org/TryGhost/Ghost/jobs/553428813 and the test that is failing is this one - https://github.com/TryGhost/Ghost/blob/cf499c3/core/test/regression/importer/importer_spec.js#L142.

Think it has to do with having moment.tz.setDefault('UTC') not being persisted globally for all moment uses.

[ichernev]

When you use a Date to feed to moment, it can't possibly know which timezone you're in. I understand the behavior changed, but you don't get any guarantees when you use a Date. Re-open if there is still an issue with later versions, and try to reference the docs (if you think we're doing something wrong).