How to calculate X days ago in javascript

Question

In my application I am accessing a remote URL and getting a JSON response like below. The JSON response has a property called created_at.

In JavaScript I need to get the current date minus(-) the created_at date and calculate how many days ago the comment was created.

How can I do that?

{  
   "id":12578834,
   "title":"Joint R&D Has Its Ups and Downs",
   "url":"http://semiengineering.com/joint-rd-has-its-ups-and-downs/",
   "num_points":1,
   "num_comments":0,
   "author":"Lind5",
   "created_at":"9/26/2016 2:28"
}

You don't need a guide - you have everything you need: `"i need to get the current date minus(-) this created_at date and calculate how many X days ago the comment was created"`. Convert that English into JS. — Shomz, Nov 24 '16 at 14:46
@Mehmet I doubt anyone needs a library for a simple subtraction. — Shomz, Nov 24 '16 at 14:48
It is a lightweight library and you can use it for all date operations. — Mehmet, Nov 24 '16 at 14:50
@shomz i have trouble in creating a date object with the created_at string and do subtraction — yasarui, Nov 24 '16 at 14:50
May be helpful - see my answer at https://stackoverflow.com/a/56832341/741251 — Nitin Jadhav, Jul 01 '19 at 08:31

Rajesh · Accepted Answer · 2020-06-17T07:42:42.590

15

You can create days and then get difference by subtracting today.getTime() - date.getTime()/NumOfMSecInDay.

Also, time part can cause some issues, so its better to strip it.

var d = {
  "id": 12578834,
  "title": "Joint R&D Has Its Ups and Downs",
  "url": "http://semiengineering.com/joint-rd-has-its-ups-and-downs/",
  "num_points": 1,
  "num_comments": 0,
  "author": "Lind5",
  "created_at": "9/26/2016 2:28"
}

var today = new Date();
var createdOn = new Date(d.created_at);
var msInDay = 24 * 60 * 60 * 1000;

createdOn.setHours(0,0,0,0);
today.setHours(0,0,0,0)

var diff = (+today - +createdOn)/msInDay
console.log(diff)

Edit:

As per @picacode, date.getTime is faster than +date. Following is a JSPer Link

edited Jun 17 '20 at 07:42

answered Nov 24 '16 at 14:49

Rajesh

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I think you don't need setHours call – maheshiv Nov 24 '16 at 14:52
@mplugjan, thanks and apologies for incorrect name – Rajesh Nov 24 '16 at 14:53
1

@maheshiv if your createdon was say `9/26/22016 20:30` and you check it at `11/24/2016 5:30` will yield `58` and `11/24/2016 21:30` will yield `59`. Hence `setHours` is required – Rajesh Nov 24 '16 at 14:55
@maheshiv - always a good idea to normalise the time. If today is DST and daysago is not, then you may get issues – mplungjan Nov 24 '16 at 14:55
I thought we can concatenate ':00' at the end and pass to Date function. But I agree with @mplungjan. – maheshiv Nov 24 '16 at 15:01
Why there are plus signs before the dates? – mcnk Jun 17 '20 at 06:56
@picacode Thats is a shorthand for `date.getTime()` – Rajesh Jun 17 '20 at 07:06
Thanks @Rajesh, I was looking into it and found out it was just turning it into a number and performance-wise it is slower than just doing `date.getTime()` I have editted the answer. For the performance test, you can check this link https://jsperf.com/new-date-timing – mcnk Jun 17 '20 at 07:14
@picacode Your JSPerf is not up to mark. I'll make a similar one which only compares `getTime` vs `+date`. Also, difference is so small, it can be ignored – Rajesh Jun 17 '20 at 07:53
@Rajesh you are right it is just 10 percent faster but anyways it is faster and more readable in my opinion. Thanks for the code. – mcnk Jun 17 '20 at 07:57

How to calculate X days ago in javascript

1 Answers1