Unix timestamps are not serialized correctly for scalar DateTime

[yamatsafi]

Describe the bug

The DateTime scalar (GraphQLDateTime) fails to convert unix timestamp, for example, 1695416400, produces a date like 1970-01-20T14:56:56.400Z. Since the Unix timestamp represents the number of seconds since January 1st, 1970 at UTC, and the Javascript Date() function's argument is in milliseconds, not seconds, the number of seconds needs to be multiplied by 1000.

const humanReadableDate = new Date(1695416400 * 1000);
// result 2023-09-22T21:00:00.000Z

To Reproduce

1- define your scalars and type

scalar DateTime;
type Event {
  id: ID!
  name: String!
  start: DateTime!
  end: DateTime!
};

2- then import and export these types in a resolver:

const {
  GraphQLDateTime
} = require('graphql-scalars');

module.exports = {
  DateTime: GraphQLDateTime,
};

3- Now you have some event resolver that returns this data:

[
  {
    id: 18797,
    start: 1695301200,
    end: 1695330000,
    name: 'Regular'
  },
  {
    id: 18798,
    start: 1695387600,
    end: 1695416400,
    name: 'Regular'
  }
]

4- The start and date will come across as 1970-01-20T14:56:56.400Z and not the correct date.

This is because the Unix timestamps aren't serialized correctly here, below:
https://github.com/Urigo/graphql-scalars/blob/v1.22.2/src/scalars/iso-date/DateTime.ts#L36

This line should be:
return new Date(value * 1000); (this matches graphql-iso-date implementation as well)

Expected behavior

Unix timestamp: 1695301200
Actual: 1970-01-20T14:55:01.200Z
Expected: 2023-09-21T13:00:00.000Z

Unix timestamp: 1695330000
Actual: 1970-01-20T14:55:30.000Z
Expected: 2023-09-21T21:00:00.000Z

Unix timestamp: 1695387600
Actual: 1970-01-20T14:56:27.600Z
Expected: 2023-09-22T13:00:00.000Z

Unix timestamp: 1695416400
Actual: 1970-01-20T14:56:56.400Z
Expected: 2023-09-22T21:00:00.000Z

Environment:

• OS: macOS (Ventura 13.5.2) / Docker in Red Hat Enterprise Linux Server release 7.9 (Maipo)
• GraphQL Scalars Version: 1.22.2
• NodeJS: 18.7.1

Additional context:

• Our stack is a nodejs with fastify v4 and the following:
• "graphql": "^16.8.0",
• "graphql-scalars": "^1.22.2",
• "@graphql-tools/schema": "^10.0.0",
• "@graphql-tools/utils": "^10.0.6",

[design1online]

I just found this same issue today. This is breaking all my bigint timestamps that I'm pulling from my DB. I had to manually add in the old package I was using so my timestamps would stop breaking everywhere.

Can we please prioritize this?