如何将日期与时刻进行比较

Question

I'm trying to compare dates from database (firebase) with NOW. I'm using moment.js and it's not working. I think it has something to do with the time zone (or UTC+01:00)...

Example.

• date1: "2016-11-20T14:00:00"
• NOW: "2016-11-20T14:49:20+01:00"

I get NOW with moment() and compare like this:

var date1 = moment("2016-11-20T14:00:00");
moment(date1).isSameOrAfter( moment() ) // returns true

The comparison is precisely one hour off... How can I fix this? AND: is there any best practice in storing and comparing dates across time zones.

Answer 1

Dates should always be saved in UTC. If you use string type the UTC date time value in ISO format.

So while saving convert from client time zone into UTC and while retrieving convert from UTC into client time zone.

Comparison should be done between two dates in the same time zone.

If the database value is in UTC and then you have to parse as .utc() while creating a moment object.

moment.utc("2016-11-20T14:00:00");

Change the NOW value to UTC before comparing.

moment.(date1).utc()

Alternatively you can change the database value from UTC to local.

 moment.utc("2016-11-20T14:00:00").local()

Keep the NOW value as is before comparing.

Answer 2

You cannot compare the date you stored in Firebase with now() as it lacks the information about your timezone.

You can store dates using Firebase.ServerValue.TIMESTAMP

For Example:

date1: Firebase.ServerValue.TIMESTAMP

This will save your time in Unix Milliseconds (time since the Unix epoch, in milliseconds) by the Firebase Database servers.

Then you can compare with new Date().getTime() this will give your device time in Unix Milliseconds.

For Example:

if(new Date().getTime() >= date1) {
    //do something
}

Hope it helps :)