Date & Timezone issue related with Front-Matter

[SukkaW]

Check List

Please check the following before submitting a new issue.

• [x] I have already read Docs page & Troubleshooting page
• [x] I have already searched existing issues and they are not helpful to me
• [x] I examined error or warning messages and it's difficult to solve
• [x] Using the latest version of Hexo (run hexo version to check)
• [x] Node.js is higher than minimum required version

The issue has been reported in

• #4239
• #3397
• #3282
• #2063

---

For example, I have a post setup as following:

# _config.yml
timezone: Asia/Shanghai

title: Hello World
date: 2020-09-29 23:00:00

Also, my machine is under the Asia/Shanghai timezone, which will also affect Node.js' timezone.

After the front-matter being processed by js-yaml, the "Date-like string" will be converted into Date object:

const jsYaml = require("js-yaml");

jsYaml.load('date: 2020-09-29 23:00:00');
// > "Tue, 29 Sep 2020 23:00:00 GMT" 

Notice that the input was converted into the UTC? Users will only fill in the front-matter with their local time, not the UTC. Thus it is not the desired behavior.

So during the processing of front-matter, Date#getTimezoneOffset has been used:

// https://github.com/hexojs/hexo-front-matter/blob/ccbdff36d151a56932418cdc6d0329d866032a1b/lib/front_matter.js#L55-L62

// Convert timezone
Object.keys(data).forEach(key => {
  const item = data[key];

  if (item instanceof Date) {
    data[key] = new Date(item.getTime() + (item.getTimezoneOffset() * 60 * 1000));
  }
});

It will result in:

"Tue, 29 Sep 2020 15:00:00 GMT"

Which is the desired behavior.

Then, during the processing pf posts, moment.timezone was used:

https://github.com/hexojs/hexo/blob/557487a2f8ab0065bf94d5a9466c54034f1db17f/lib/plugins/processor/post.js#L80-L82 https://github.com/hexojs/hexo/blob/557487a2f8ab0065bf94d5a9466c54034f1db17f/lib/plugins/processor/common.js#L51-L60

If the config.timezone is configured correctly, there will be no differences between before and after timezone():

"Tue, 29 Sep 2020 15:00:00 GMT"
// There's no differences

A demo can be found here: https://runkit.com/sukkaw/5f732261a7aac8001a42bcc4

Date#getTimezoneOffset: -480
Date parsed by js-yaml: Tue, 29 Sep 2020 23:00:00 GMT
Date after calculating the timezone offset: Tue, 29 Sep 2020 15:00:00 GMT
Date after moment-timezone: Tue, 29 Sep 2020 15:00:00 GMT
Date after moment-timezone (without pre offset): Tue, 29 Sep 2020 15:00:00 GMT // Will be discussed later

So, what about a different timezone environment? For example, the CI environment. Its timezone will not be Asia/Shanghai.

So here is another demo: https://repl.it/repls/LividBewitchedControlflowgraph#index.js

Date#getTimezoneOffset: 0 // See? It is not -480 anymore, it is now 0
Date parsed by js-yaml: Tue, 29 Sep 2020 23:00:00 GMT
Date after calculating the timezone offset: Tue, 29 Sep 2020 23:00:00 GMT // It is now wrong
Date after moment-timezone: Tue, 29 Sep 2020 15:00:00 GMT // But it is still correct
Date after moment-timezone (without pre offset): Tue, 29 Sep 2020 15:00:00 GMT // Will be discussed later

As you can see, Date after calculating the timezone offset is now wrong, while Date after moment-timezone is still correct. That's because timezone() takes getTimezoneOffset into consideration.

---

So, what about removing "getTimezoneOffset" completely?

Here goes Date after moment-timezone (without pre offset). It is generated without using Date#getTimezoneOffset, and the result is still correct. It also means it is not affected by the environment (no `Date#getTimezoneOffset being used).

By eliminating the Node.js timezone affection (only dependents on users' config.timezone configuration) the timezone issue should be solved.

[SukkaW]

cc @YoshinoriN @ItsZero @stevenjoezhang @curbengh

---

So far I just assume those issues were caused by their machines' timezones are inconsistent with their hexo configurations.

[curbengh]

So, what about removing "getTimezoneOffset" completely?

+1, Hexo shouldn't need to query the host machine's timezone, config.timezone should be the canonical timezone.

---

There is still a need to query host's timezone since config.timezone is empty by default. Host's timezone should be ignored if config.timezone is specified.

---

Another complication is that it is also possible to specify timezone in front-matter, e.g. 2013-02-08 09:30:26.123+07:00.

Perhaps we can prioritise like this:

1. Front-matter's timezone
2. config.timezone
3. host's timezone

[SukkaW]

There is still a need to query the host's timezone

@curbengh

It appears that there is no way we could get the timezone name directly (If so, we could use it as a default value during hexo config processing). The only thing we get is getTimezoneOffset.

[SukkaW]

@curbengh

We can use JavaScript built-in object Intl:

Intl.DateTimeFormat().resolvedOptions().timeZone
// UTC
// Asia/Tokyo
// etc.

We can use it for the default timezone in config.