JavaScript UTC Date Comparison Bug

Question

I'm comparing UTC dates and getting this very weird result.

now is definitely bigger than start as far as I can tell, yet the statement returns false.

var start = new Date('2021-01-29T21:00:00.000Z');
var now   = new Date('2021-01-29T00:16:47.797Z');

console.log(now >= start); //false

question from:https://stackoverflow.com/questions/65947371/javascript-utc-date-comparison-bug

Answer 1

Youre comparing 12:16:47 in the morning, or 45 minutes till 1am against 9pm in the same day. Chronologically this makes perfect sense. If you were to change "now" to the day after, referencing 12:16am of the following day, it returns true.

var start = new Date('2021-01-29T21:00:00.000Z');
var now = new Date('2021-01-29T00:16:47.797Z');

console.log(now >= start); //false

var start = new Date('2021-01-29T21:00:00.000Z');
var now = new Date('2021-01-30T00:16:47.797Z');

console.log(now >= start); //true