使用moment.js比较来自不同时区的时间

Question

I have a Node.js server that triggers function based on timezones. Specifically, I'm using moment-timezone and from a fixed date and time input I need to trigger action at that same input but in different time zones.

So if I set in my server that the action should be triggered at 1:00 pm UK time and the user is in New York, I want the action to be triggered at 1:00 pm in New York.

That's what I am doing now:

exports.time_to_trigger = function(hour, date) {
    var user_timezone = "Asia/Tokyo";

    // create date object from date + hour strings
    var dateObj = moment(date + hour, process.env.DATE_FORMAT + " HH:mm a");

    // create offset
    var max_value = moment(dateObj).add(3, 'minutes');
    var low_value = moment(dateObj).add(-3, 'minutes');

    console.log(max_value); // -> moment("2018-01-25T13:03:00.000")
    console.log(low_value); // -> moment("2018-01-25T12:57:00.000")

    // get the now value of the user timezone
    var user_now = moment.tz(moment(), user_timezone);

    console.log(user_now); // -> moment.parseZone("2018-01-24T13:01:00.038+09:00")

    console.log(user_now.isAfter(low_value)); // -> false
    console.log(user_now.isBefore(max_value)); // -> true

    return (
        user_now.isAfter(low_value) &&
        user_now.isBefore(max_value)
    )
}

As you can see from the comment, this is not working as the comparison with isAfter and isBefore take into consideration the time zone that I converted on purpose not to have this problem. How can I solve this?

Answer 1

Your issue is that you use timezone to get user_now but not to create dateObj . So dateObj is missing the timezone offset and your 2 dates are not comparable as you would wish.

To have all your dates on the same timezone:

// create date object from date + hour strings
var dateObj = moment.tz(date + hour, process.env.DATE_FORMAT + " HH:mm a", user_timezone);