momentjs - Trouble using utcoffset with Chart.js

Question

I'm trying to use Chart.js with a datetime x axis, and I need to adjust all my values by subtracting 5 hours. Here's some of my code:

var timeFormat = 'MM/DD HH:mm';

time: {
  format: timeFormat,
  tooltipFormat: 'll',
  parser: function(utcMoment) {
    return moment(utcMoment).utcOffset(5, true);
  }
},

Without the parser function, my values are normal (10:00, January 10, 2021), but with the parser function, for some reason my values are set back all the way to 2001. Yes two-thousand-and-one.(10:00, January 10, 2001) Note that the time is not actually changed (So two errors: 1.time not adjusted when it should be. 2:years adjusted when it shouldn't be). Why could this be?

question from:https://stackoverflow.com/questions/65649475/trouble-using-utcoffset-with-chart-js

Answer 1

I will assume that the reason you want to roll it back by 5 hours is because of a timezone difference. If that's the case, you should use moment-timezone instead of moment.

With that said, subtracting 5 hours from the current date is actually simpler than what you're doing.

Before feeding a date into moment, you need to convert it to the js Date object like so: new Date('2021-01-10 00:00:00'). Since your parser function accepts the date in m/d H:M format, you would need to append the year to it first.

So here is how your code should look:

parser: function(utcMoment) {
    const new_date = utcMoment.split(' ')[0] + '/' + (new Date().getFullYear()) + ' ' + utcMoment.split(' ')[1];
    return moment(new Date(new_date)).subtract({hours: 5})
}