compare two dates on different days, return specific date with less hours and minutes-CodePudding

I have two dates that are UTC

"2022-11-01T22:16:19.844Z" // <-- in the past but later in the day

"2022-11-08T20:16:19.844Z" // <--- in the future but earlier in the day

The first date is < the second date BUT it is later in the day...

I am trying to return the date the is the earliest in the day ex the least amount of hours and minutes... I dont want to return the date that is in the past, ONLY the date that occurs earliest in the day

I have tried

const date_a = new Date("2022-11-01T22:16:19.844Z").getTime()

const date_b = new Date("2022-11-08T20:16:19.844Z").getTime()

//this is always comparing the ENTIRE date, which will return date_a as the lessor when in reality what I want is date_b because it is actually occuring earlier in the day...

CodePudding user response：

Time Sorting

When doing date comparisons it's often simpler to compare strings rather than doing a numerical comparison of hours, minutes, seconds, and milliseconds. And for this problem we could compare the UTC time string of each date, which can be parsed from the date using:

.toISOString() --> "2022-11-10T20:16:19.843Z"
.split("T") --> ["2022-11-10", "20:16:19.843Z"]
.pop() --> "20:16:19.843Z"

And then we sort the time strings using .localeCompare() and return the first element of the array:

let value = dates.sort((a,b) => 
  a.toISOString().split("T").pop().localeCompare(
    b.toISOString().split("T").pop()
  )
)[0];

The code could be simplified for use with local times by using .toTimeString() which wouldn't require the split and pop steps.

Snippet

let dates = [
  new Date("2022-11-10T20:16:19.843Z"),
  new Date("2022-11-01T22:16:19.844Z"),
  new Date("2022-11-08T20:16:19.844Z")
];

let value = dates.sort((a,b) => 
  a.toISOString().split("T").pop().localeCompare(
    b.toISOString().split("T").pop()
  )
)[0];


console.log(value);

CodePudding user response：

You can use Date.prototype.setYear(), setMonth() and set Day() and set the first part of both dates to 0, and then do the comparison.