UTC date parsing issue

[raajnadar]

Problem

Hermes

new Date("Friday, 02-Aug-2019 07:14:03 UTC");
Date { NaN }

JSC

new Date("Friday, 02-Aug-2019 07:14:03 UTC");
2019-08-02T07:14:03.000Z

Chrome browser dev tools

new Date("Friday, 02-Aug-2019 07:14:03 UTC"));
Fri Aug 02 2019 12:44:03 GMT+0530 (India Standard Time)

Solution

Add support for this date format

Additional Context

It looks similar to this issue ticket #219

[raajnadar]

Can we get some attention to this issue? Or else I won’t be able to upgrade to Expo SDK 47 which uses RN 0.70

[jpporto]

Hi,

Thanks for your feedback, and apologies for the delayed response. This is in the teams radar, but even if we were to add this support today, RN 0.70 has already shipped, and thus this support won't be available in that version.

John Paul

[raajnadar]

I thought this can be sent in a patch release, once this is solved in Hermes, We can ask in the react native releases discussion, if not I am ok to wait for some time, as only one project is blocked due to this, and AFAIK RN v0.70 Hermes is the default so it cannot be turned off, currently I have turned off Hermes to use the v0.69

[jpporto]

Hi,

Hermes being the default doesn't mean it is required. You can still disable it in your project (see this). Also, note that Hermes is only the default for new projects: Existing projects should be using their engine of choice. If not, reach out to the RN folks as this is probably a bug.

John Paul

[fbmal7]

Hi @raajnadar we put together a fix which should be landing soon.

won’t be able to upgrade to Expo SDK 47

If you can, could you elaborate a bit on this point? It would be good to know how broadly this inconsistency between JSC and Hermes could currently be affecting users.

[raajnadar]

@fbmal7 I had a misunderstanding, I thought RN 0.70+ required Hermes to be enabled, after clearly reading the docs I found it is only default for the new apps.

Expo SDK 47 will add support for RN 0.70.3 in the Expo Go app, so I thought I won't be able to upgrade, but I was wrong

[fbmal7]

Okay, but either way at one point this date behavior was causing some incompatibility, correct? I was just interested in learning more about how this was preventing you from using Hermes. But the fix has been shipped in a26472f :)

[raajnadar]

Actually, when I enabled Hermes it was leading to an app crash, so I turned off the Hermes and build the apk

And it crashed only on the apk or aab, not in the dev environment so it was tricky to debug the issue

[fbmal7]

So then, how did you determine that Expo was depending on Hermes supporting this Date format?

[raajnadar]

I strictly follow the Expo SDK version to upgrade my React Native version, in Expo SDK 47, RN 0.70 is planned, previously I had confusion about Hermes being the default which is clear now.

I use Expo Go for development

The app crashed when Hermes was enabled. I had to run the expo in prod mode to get the crash logs. It crashed because I was passing the date to the Date Fns library’s parseISO() method

[fbmal7]

So you were providing the Date yourself? I thought you were saying Expo itself produced Dates in that format, thus making Expo and Hermes incompatible for some version of Expo.

[raajnadar]

No, the date was returned by my PHP server, not sure why the backend dev was sending this format, we usually get ISO format which works very well with Hermes.

To be clear Expo is my dev tool, I am using Hermes in every application that is run using Expo Go, we found this date issue only in 1 project which was sending a different date format, with ISO there are no issues.