Time zones and date strings

Published July 2, 2021

code

Recently, I ran into an issue with time zones and date strings. I was running an Express app and the toDate sanitizer from validator.js via express validator.

Just for illustrative purposes, let's say I want to delete the oldest users that fall within a specific date range by making a request like this.

axios.delete('/users', {
  startDate: '2020-06-01',
  endDate: '2020-09-01'
})

My route definition could look like this.

app.delete('/users',
  body('startDate').toDate(),
  body('endDate').toDate(),
  (req, res) => {
    const startDate = req.body.startDate
    const endDate = req.body.endDate

    // Delete all users where their created_at
    // is between startDate and endDate
  }
)

Then, I can expect startDate and endDate to be instances of the Date object. If you console log them you should see this.

startDate 2020-06-01T00:00:00.000Z
endDate 2020-08-01T00:00:00.000Z

Since there was no time portion in the request, the Date object interpreted it as midnight UTC. If there were any users that have a created_at column of 05/31/2020 at 9:00pm Eastern, they would be incorrectly deleted. The reason is because their created_at timestamp would be stored in the database as 2020-06-01T01:00:00.000Z UTC.

One solution to this problem would be to pass the timezone in the request like this.

axios.delete('/users', {
  startDate: '2020-06-01',
  endDate: '2020-09-01',
  timezone: 'America/New_York'
})

Then, to remove the toDate sanitizers.

app.delete('/users',
  (req, res) => {
    // ...
  }
)

You can manually parse the dates using a library like Luxon.

import { DateTime } from 'luxon'

app.delete('/users', (req, res) => {
  const timezone = req.body.timezone
  const startDate = DateTime.fromFormat(req.body.startDate, 'yyyy-MM-dd', { zone: timezone })
    .startOf('day')
    .toUTC()
    .toJSDate()
  const endDate = DateTime.fromFormat(req.body.endDate, 'yyyy-MM-dd', { zone: timezone })
    .startOf('day')
    .toUTC()
    .toJSDate()

  // ...
})

Now if you console log the start and end date, you should get the correct times.

startDate 2020-06-01T04:00:00.000Z
endDate 2020-08-01T04:00:00.000Z