Develop Reference

Javascript: how to convert a UTC date to local one?

Looks like a very simple thing to do? Not afrer reading this http://dygraphs.com/date-formats.html - what a mess!
var time_utc="2016-04-25 20:19:00.306671";
document.write("Local date:"+new Date(time_utc+" UTC")); // Firefox 44.0.2: Invalid Date
How do I print a date in above format adjusted to local time?

The article you provided mentions halfway through the page,
Using hyphens (-) instead of slashes (/) works in WebKit browsers, but
not in IE or FF. Beware the UTC parse of YYYY-MM-DD!
As well as,
Don't try to specify milliseconds. Only recent versions of Chrome will
understand you.
With the date 2016-04-25 20:19:00.306671 you use hyphens and milliseconds. You could modify your time_utc string a bit to make it compatible like so,
var time_utc = "2016-04-25 20:19:00.306671";
time_utc = time_utc.replace(/-/g, "/");
time_utc = time_utc.split(".").shift();
var d = new Date(time_utc);
d.toString();
The above code outputs,
Mon Apr 25 2016 20:19:00 GMT+0200 (CEST)

Have you looked into Moment.js? http://momentjs.com/ It's a handy date-object wrapper that makes date object manipulation easy. Particularly, the local() function provided will give you what you need here.
All you have to do is install moment from npm and then include it in your js file at the top like this:
var moment = require("moment");
Then to change your time_utc variable to local all you have to do is:
var time_utc="2016-04-25 20:19:00.307";
document.write("Local date:"+moment(time_utc).local());
As someone advised me before, it is not wise to include an entire library for a simple, one time function. As a disclaimer, my work requires me to do many date-time calculations and conversions throughout a large project, so including a library for ease is much preferred in my case. However, if you only have to use it this one time, my answer may not be the best.

If you use moment.js, you can use:
var time_utc = "2016-04-25 20:19:00.306671";
var localDate = moment.utc(time_utc).local();

You need append UTC to the string before converting it to a local date in js:
var date = new Date('25/04/2016 4:52:48 PM UTC');
date.toString() // "Mon Apr 25 2016 09:52:48 GMT-0700 (PDT)"

How do I convert to browser timezones using phstc dateFormat?

EDIT : Btw, I have no idea why this question was marked as a duplicate. The answers in the original question does not work for me. i.e, getting wrong results and stuffs. Furthermore, none of the answers deal with phstc's dateFormat function. Do correct me if I'm wrong. Btw, I have solved this question. Do take a look at my answer.
I want to change a UTC datetime to my browser's timezone. I'm using phstc's dateFormat in pure javascript form. Let's say I convert a datetime of 2014-06-27 07:11:16 using a javascript Date() function. The result I got was
Fri Jun 27 2014 07:11:16 GMT+0800 (Malay Peninsula Standard Time)
Then when I use phstc's toBrowserTimeZone function, it still returns me the same datetime. I wanted to get something like 2014-06-27 15:11:16
Here is the code below:
var originalDateTime = new Date(`2014-06-27 07:11:16`);
alert(DateFormat.format.toBrowserTimeZone(originalDateTime,"yyyy/MM/dd HH:mm:ss"));

According to this statement in phstc's dateFormat page,
value = String representing date in ISO time (“2013-09-14T23:22:33Z”) or String representing
default JAXB formatting of java.util.Date (“2013-09-14T16:22:33.527-07:00”) or String representing
Unix Timestamp (Sat Sep 14 2013 16:22:33 GMT-0700 (PDT)) or javascript date object.
JS Date object should work but unfortunately, it didn't. Well, I got it fixed by changing the datetime to other formats stated above first before calling the toBrowserTimeZone() function. For example,
var originalDateTime = DateFormat.format.date('2014-06-27 07:11:16',"yyyy-MM-ddTHH:mm:ssZ");
var newDateTime = DateFormat.format.toBrowserTimeZone(originalDateTime);

Date format conversion javascript

Consider if we have a date in the format Sat Jul 28 2012 , is there a general a function to convert it in to any wanted format??
say for example 28-07-2012,
deciding the separators like - or /

Javascript's Date object has lots of different versions of toString and different getters, so it should be pretty easy to get the output you want. Scroll down through this documentation to see some of your options. They have pretty good examples too if you click on them.
In addition, the Date constructor is fairly good at taking in most strings and converting it.
var myDate = new Date("Sat Jul 28 2012");
alert(myDate.toLocaleDateString());
Or use the different getters and string concatenation wrapped in a function to make your own.

You can write a function to do it, i dont think there is a Native method:
function convert(dateObj) {
var format = dateObj.getFullYear()+"-";
format += dateObj.getMonth()+"-";
format += dateObj.getDate();
return format;
}
you can customize it however you want. here is the list of methods for the date object

Javascript only outputs it into the standard format you provided above. You can try using the getDate(), getDay(), getMonth() methods (among others) to extract the necessary data and convert it to your liking.
Please refer to W3Schools' description of the JavaScript Date object.

Is there a simple conversion for this datetime format?

I'm retrieving data from a JSON feed using jQuery and as part of the feed I'm getting 'datetime' attributes like "2009-07-01 07:30:09". I want to put this information into a javascript Date object for easy use but I don't believe the Date object would recognize this kind of format if I simply plugged it into the constructor. Is there a function or maybe a clever trick I can use to quickly break down this format into something the Date object can recognize and use?

The "date" attribute you are retrieving from that webservice is not a real Date, as it is not a recognized date format.
The easiest way to handle it as a Date object would be to replace the empty space with a "T":
var receivedDate = "2009-07-01 07:30:09";
var serializedDate = new Date(receivedDate.replace(" ", "T"));
alert(serializedDate);
This is not the most correct, as it is not handling timezones, but in most cases will work.

See this and this.
input = "2009-07-01 07:30:09";
var res = input.match(/([\d\-]+) (\d+):(\d+):(\d+)/);
date = new Date(Date.parse(res[1]));
date.setHours(res[2]);
date.setMinutes(res[3]);
date.setSeconds(res[4]);
console.log(date);
Edit: My original answer was
t = new Date(Date.parse("2009-07-01 07:30:09"));
which did not throw any error in chrome but all the same incorrectly parsed the date. This threw me off. Date.parse indeed appears to be quite flaky and parsing the complete date and time with it is probably not very reliable.
Edit2: DateJS appears to be a good solution for when some serious parsing of text to date is needed but at 25 kb it is a bit heavy for casual use.

var str="2009-07-01 07:30:09";
It depends on the time zone,
and if the date string has subtracted 1 for the month.
If it is GMT time, and the 07 means July and not August:
var str="2009-07-01 07:30:09";
var d=new Date(), time;
str=str.split(/\D0?/);
str[1]-=1;
time=str.splice(3);
d.setUTCFullYear.apply(d,str);
d.setUTCHours.apply(d,time)
alert(d)
/* returned value: (Date)
Wed Jul 01 2009 03:30:09 GMT-0400 (Eastern Daylight Time) or local equivilent
*/

This may be a bit cumbersome, but the JavaScript Date object will take an argument list of YYYY,MM,DD,HH,MM,SS. Parse out the date value and pass it to a Date constructor, e.g.
var splitDT= '2009-07-01 07:30:09'.split(' '); // ['2009-07-01','07:30:09']
var d= splitDT[0].split('-');
var t= splitDT[1].split(':');
alert( (new Date(d[0],d[1],d[2],t[0],t[1],t[2])) );
Bah. Had to use the array index values instead. Yeah, that's a mess. But it works.

Java date format to JavaScript date format

I would like to be able to convert a Java date format string, e.g. dd/MM/yyyy (07/06/2009) to a JavaScript date format string, e.g. dd/mm/yy (07/06/2009).
Has anyone done this before, or got any idea where I might find some code that already does this?
Edit:
Thanks for all the replies but now I realize my mistake and possibly why so many of you were struggling to understand the question; JavaScript doesn't have a built in date formatting ability. I am using the jQuery UI datepicker and I have been setting its date format, assuming it would be calling a standard JS function at some point, not using its own library! When I googled for formatting strings I jumped straight to the tables of what letters could be used, skipping the bit at the beginning explaining how to use the script.
Anyway I'll have to go ahead and possibly write my own I guess, converting a Java date format string into a jQuery date format string (or as close as possible) - I am working on the i18n of our product and have created a java class that stores the preferred date format string used throughout the application, my intention was to also have the ability to supply any jsps with the format string that is equivalent in JS.
Thanks anyway.

If you just need to pass a date from Java to JavaScript, the best way to do it, I think, would be to convert the Java date to milliseconds using date.getTime(), create a JavaScript date initialized with this milliseconds value with new Date(milliseconds)and then format the date with the means of the JavaScript Date object, like: date.toLocaleString().

You could use my plugin jquery-dateFormat.
// Text
$.format.date("2009-12-18 10:54:50.546", "dd/MM/yyyy");
// HTML Object
$.format.date($("#spanDate").text(), "dd/MM/yyyy");
// Scriptlet
$.format.date("<%=java.util.Date().toString()%>", "dd/MM/yyyy");
// JSON
var obj = ajaxRequest();
$.format.date(obj.date, "dd/MM/yyyy");

A similar topic has been answered here:
Converting dates in JavaScript
I personally have found this to be a rather large pain and took the author's suggestion and used a library. As noted, jQuery datepicker has one that is a viable solution if you can afford the overhead of download for your application or already using it.

Check out moment.js! It's "A lightweight javascript date library for parsing, manipulating, and formatting dates". It is a really powerful little library.
Here's an example...
var today = moment(new Date());
today.format("MMMM D, YYYY h:m A"); // outputs "April 11, 2012 2:32 PM"
// in one line...
moment().format("MMMM D, YYYY h:m A"); // outputs "April 11, 2012 2:32 PM"
Here's another example...
var a = moment([2012, 2, 12, 15, 25, 50, 125]);
a.format("dddd, MMMM Do YYYY, h:mm:ss a"); // "Monday, March 12th 2012, 3:25:50 pm"
a.format("ddd, hA"); // "Mon, 3PM"
a.format("D/M/YYYY"); // "12/3/2012"
Also, its worth mentioning to checkout date.js. I think the two libraries complement each other.

This JavaScript library should be able to help you.
http://plugins.jquery.com/project/fIsForFormat
(I don't know why they have it as a jQuery Plugin, because it works standalone.)
You'd simply split the original formatted date into its individual elements and then create a new Date Object with those elements. Then, use this library's "Date.f()" method to output it into any format you could want.
For example:
var dateOld = "11/27/2010",
dateArr = date1.split("/"),
dateObj = new Date(dateArr[2], dateArr[0], dateArr[1]),
dateNew = dateObj.f("MMM d, yyyy");
document.write("Old Format: " + dateOld + "<br/>New Format: " + dateNew);

This works fine for me:
<%
Date date = Calendar.getInstance().getTime();
%>
<script>
var d = new Date(<%=date.getTime()%>);
alert(d);
</script>

I suggest you the MomentJS with this Plugin that allow you to convert a Java pattern to a JS pattern (MomentJS)

On Java Side
I recommend passing an Instant string which conforms to ISO 8601 standard.
import java.time.Instant;
class Main {
public static void main(String[] args) {
Instant instant = Instant.now();
// You can pass the following string to JavaScript
String strInstant = instant.toString();
System.out.println(strInstant);
// If the number of milliseconds from epoch is required
long millis = instant.toEpochMilli();
System.out.println(millis);
}
}
Output from a sample run:
2022-12-31T09:40:52.280726Z
1672479652280
ONLINE DEMO
Learn more about the modern Date-Time API from Trail: Date Time.
On JavaScript Side
Now, you can parse the ISO 8601 string on the JavaScript side simply by passing it as a parameter to Date constructor. You can also instantiate the Date object with the number of milliseconds from the epoch.
var date = new Date("2022-12-31T09:40:52.280726Z");
console.log(date.toISOString());
// Or if the number of milliseconds from epoch has been received
date = new Date(1672479652280);
console.log(date.toISOString());

The javascript code in this page implements some date functions and they "use the same format strings as the java.text.SimpleDateFormat class, with a few minor exceptions". It is not the very same as you want but it can be a good start point.

If you just want to format dates my date extensions will do that well - it also parses data formats and does a lot of date math/compares as well:
DP_DateExtensions Library
Not sure if it'll help, but I've found it invaluable in several projects.

If you are using java, take a look at the Simple Date Format class.