jsfiddle example: https://jsfiddle.net/xhzce36p/1/
To be more specific, what is happening is the date defaults to a time of midnight, so 5/1/2019 is actually 5/1/2019 12:00:00 AM
If you subtract a few hours (four, in my case) because you're in a timezone that is not the UTC+0 timezone, the date becomes 4/30/2019 08:00:00 PM. If you're only displaying the date and not the time, you'll see 4/30/2019. It probably won't be obvious when you see it. All you see is that your date is off by a day. Well, now you know why.