Datetimes in Javascript

Question

Im not particularly skilled when it comes to working with datetimes in js. I have a JSON object that has some datetime fields formatted like YYYY-MM-DDTHH:MM:SS now I have to put this in HH:mm AM/PM and I came up with:

var d = Date.parse('2013-04-17T13:05:00');
var date = new Date(d);
var hrs = date.getUTCHours();
var min = date.getUTCMinutes();
var meridian;
if(hrs > 12){
 hrs -= 12;
 meridian = 'PM';
}
else {
 meridian = 'AM';
}
if (min < 10) {
 min = "0"+min;
};
var time = hrs+":"+min+" "+meridian;

Is there a better way to accomplish this?

• Marc B: nope. that's about it. the JS datetime object has essentially NO output formatting capabilities built into it.
• nullability: There is a .toLocaleFormat method, but alas, it only works in Firefox. You'd need to use a library if you want something easier, but unless you need to juggle timezones it's usually more efficient to just write your own formatter for your particular case.
• Jace Rhea: The better way is to use a well tested date library. Moment.js is a good place to start.
• Matt Johnson-Pint: ISO date parsing is not available in every JS environment. See here. Use moment.js. It works everywhere.
• LouieV: @MattJohnson I just realized that :( honestly I wanted to stay away from having to add another library as the app has a lot already

Answer 1

try moment.js, this library has a ton of functionality built in.

http://momentjs.com/

moment(String, String);
moment("12-25-1995", "MM-DD-YYYY");

"hA" is the righ format for "3PM" format

• Colin DeClue: Any time someone is using date times with Javascript, I recommend moment.js. It makes lives better.
• Rayweb_on: Yes and its pretty easy to use, but also offers a lot of functionality

Answer 2

A different answer for a different approach

has some datetime fields formatted like YYYY-MM-DDTHH:MM:SS now I have to put this in HH:mm AM/PM

As you know the formatting, you can take the parts you want directly from the datetime String, avoiding the use of a Date instance or library all together.

var stamp = '2013-04-17T13:05:00',
 hrs = +stamp.slice(11, 13), // 13
 min = +stamp.slice(14, 16); // 5

then continue as before from here.

Answer 3

This is overkill, but I recently went out of my way to make my own function just for things like this

var easyDate = (function () {
 var days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'],
 months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'],
 thstndrd = ['th', 'st', 'nd', 'rd', 'th', 'th', 'th', 'th', 'th', 'th'],
 toDate = function () {return new Date(Date.UTC(this.yyyy, this.MM - 1, this.dd, this.hh, this.mm, this.ss, this.ms));},
 toLocaleDate = function () {return new Date(this.yyyy, this.MM - 1, this.dd, this.hh, this.mm, this.ss, this.ms);},
 UTC = function UTC(d) {
 return {
 ms: d.getUTCMilliseconds(),
 ss: d.getUTCSeconds(),
 mm: d.getUTCMinutes(),
 hh: d.getUTCHours(),
 dd: d.getUTCDate(),
 MM: d.getUTCMonth() + 1,
 yyyy: d.getUTCFullYear(),
 dow: d.getUTCDay(),
 toDate: toDate,
 toLocaleDate: toLocaleDate
 }
 },
 easyDate = function easyDate(d) {
 var o = UTC(d);
 return {
 dd: '' + o.dd,
 th: thstndrd[o.dd % 10],
 day: days[o.dow],
 MM: '' + o.MM,
 month: months[o.MM - 1],
 year: '' + o.yyyy,
 am: o.hh < 12 ? 'a.m.' : 'p.m.',
 hh: o.hh < 10 ? '0' + o.hh : '' + o.hh,
 h: '' + (o.hh % 12 || 12),
 mm: o.mm < 10 ? '0' + o.mm : '' + o.mm,
 ss: o.ss < 10 ? '0' + o.ss : '' + o.ss,
 ms: ('00' + o.ms).slice(-3),
 UTC: o
 };
 };
 easyDate.UTC = UTC;
 easyDate.delta = function (then, now) {
 var o, p, dir = -1;
 now || (now = new Date());
 if (now >= then) o = UTC(now), p = UTC(then);
 else o = UTC(then), p = UTC(now), now = then, dir = 1;
 o.dir = dir;
 o.dow = p.dow;
 o.ms = o.ms - p.ms;
 o.ss = o.ss - p.ss;
 o.mm = o.mm - p.mm;
 o.hh = o.hh - p.hh;
 o.dd = o.dd - p.dd;
 o.MM = o.MM - p.MM;
 o.yyyy = o.yyyy - p.yyyy;
 // fix negatives
 if (o.ms < 0) --o.ss, o.ms = (o.ms + 1000) % 1000;
 if (o.ss < 0) --o.mm, o.ss = (o.ss + 60) % 60;
 if (o.mm < 0) --o.hh, o.mm = (o.mm + 60) % 60;
 if (o.hh < 0) --o.dd, o.hh = (o.hh + 24) % 24;
 if (o.dd < 0) { // months have different lengths
 --o.MM;
 now.setUTCMonth(now.getUTCMonth() + 1);
 now.setUTCDate(0);
 o.dd = (o.dd + now.getUTCDate()) % now.getUTCDate();
 }
 if (o.MM < 0) --o.yyyy, o.MM = (o.MM + 12) % 12;
 return o;
 };
 return easyDate;
}());

And using it

var o = easyDate(new Date());
o.month + ' ' + o.dd + o.th + ', ' + o.h + ':' + o.mm + ' ' + o.am;
// "June 18th, 7:30 p.m."

If you noticed the thing called easyDate.delta in the code, yep, it supports calculating differences in time, too. If you just want to run getUTC* for everything then you have easyDate.UTC. :)

• Paul S.: If you're wondering why I did it when there is moment.js, I like to know exactly what is happening, why, and only have what I need (I like Objects more than Strings). This also minifies down to 1.4 kb with closure compiler (a quarter the size of moment).
• Matt Johnson-Pint: The OP asked about parsing an ISO8601 formatted string. Your code doesn't do that at all.
• Paul S.: I understood the question Is there a better way to accomplish this? to be about formatting Date (or skipping Date entirely), not about how to convert ISO 8601 to Date.
• Matt Johnson-Pint: Umm... not sure how you missed it, he said quite clearly: "I have a JSON object that has some datetime fields formatted like YYYY-MM-DDTHH:MM:SS"
• Paul S.: @MattJohnson He also gets from YYYY-MM-DDTHH:MM:SS to a Date without error in 2 lines. Yes, it could be done in one with just a new Date('2013年04月17日T13:05:00');, but he's demonstrated that he is able to parse it.