Develop Reference

Troubleshooting a Date That Won't Parse in Javascript

Getting date properties back from a C# web API that seemed fine but ran into issues when plugging it into DevExtreme DateBox. It was throwing an error of 'getFullYear is not a function' so I checked the dates against this function I found here -
let r: any = http.post('/get', { Param1: 2, Param2: 1 });
console.log(r.StartDate);
console.log(this.isValidDate(r.StartDate));
r.StartDate = new Date(r.StartDate);
r.EndDate = moment(r.EndDate);
console.log('Start Date', this.isValidDate(r.StartDate));
console.log('End Date', this.isValidDate(r.EndDate));
isValidDate(d: any): void {
if (Object.prototype.toString.call(d) === "[object Date]") {
console.log('it is a date');
if (isNaN(d)) { // d.getTime() or d.valueOf() will also work
console.log('date object is not valid');
} else {
console.log('date object is valid');
}
} else {
console.log('not a date object');
}
}
StartDate: "/Date(1657512000000)/"
not a date object
undefined
it is a date
date object is not valid
Start Date undefined
not a date object
End Date undefined
Not sure why this hasn't come up before with this API but didn't want to look to DevExpress given that I can't produce a valid date.

I'm providing this answer to demonstrate one way to parse out the timestamp in the string you have of the following format, inferred by console.log(r.StartDate); ... /Date(TS)/:
// Provided the date has the following structure in a string
var anyStartDate = "/Date(1657512000000)/";
// Prepare to parse it out by getting the positions of the parentheses
var openParens = anyStartDate.indexOf("(");
var closeParens = anyStartDate.indexOf(")");
// Parse out the timestamp
var timeStampStr = anyStartDate.substring(openParens + 1, closeParens);
console.log( timeStampStr ); // 1657512000000
// Convert timestamp to an int. You can do this when you create the obj, but I am separating it here for explanation purposes.
var timeStampInt = parseInt( timeStampStr );
// Now create a date object
var dateObj = new Date( timeStampInt );
console.log( dateObj );
// (on the machine I'm on):
// Outputs: Mon Jul 11 2022 00:00:00 GMT-0400 (Eastern Daylight Time)
// Or outputs: 2022-07-11T04:00:00.000Z
Now I don't know which library(ies) you are using to handle dates so I just went with the native Date object. You can use this SOLUTION however on further insights to apply it to your code.
The point is once the timestamp is extracted, it can be then used to create a Date object, and thus utilize all the methods that are inherent to that class.
In terms of the "timezone", to get it to UTC, it's already in UTC but javascript formats it to your computer's locale. Internally it's still UTC. There's a way to display it as strictly UTC which is in the docs.
`

Javascript Cannot use .now() on date string

So I wanted to compare two dates inside a post object. I tried to compare the date objects, but that returned NaN. Then I tried converting it to milliseconds since 1970 by using .now() on these dates, but it returned the following error:
It happens: TypeError: a.date.now is not a function
I tried typeof a.date and this returned string. I don't know why I can't use the .now() method. Can someone help me?
the whole function inside of angular service
getPosts(section) {
return this.http.get(url + '/forum/getPosts/' + section )
.map( (posts: any) => {
// posts should be ordened based on latest replies. If there are no replies yet, we compare it to the date
// of the original post
posts.obj.sort((a, b) => {
const aHasReplies = a.replies.length !== 0;
const bHasReplies = b.replies.length !== 0;
if (aHasReplies && bHasReplies ) {
return a.replies.slice(-1, 1)[0].date - b.replies.slice(-1, 1)[0].date;
} else if ( aHasReplies && !bHasReplies) {
return a.replies.slice(-1, 1)[0].date - b.date;
} else if ( !aHasReplies && bHasReplies) {
return a.date - b.replies.slice(-1, 1)[0].date;
} else {
console.log(a.date.now());
return a.date - b.date;
}
});
return posts;
});
}

It should be object, not string, if that's what you meant, because there is no "date string".
Other than that try:
new Date(a.date).getTime()
Because .now is a static method, you always use it as Date.now()
This means, that Date.now() always returns milliseconds elapsed since the UNIX epoch.
For converting to unix time use getTime.
If you want to compare them, compare two dates without conversion.
But keep in mind, that unix time is in seconds, and javascript method return in milliseconds. If you need exactly unix time, divide by 1000.

You can compare two dates in the year-month-day format (yyyy-mm-dd) using regular javascript comparators such as < and > etc

I suggest use moment.js library (https://momentjs.com/docs/) to parse Date from String.
So you can have some thing like
let date = moment(a.date)

In moment.js, is it possible to have a date-time string and keep the date but change the time?

I'm using moment.js and want to update a date-time string with a new user-entered time. The date has not changed, only the time. There is no timezone change, just that the hour and minute values have possibly been altered.
How would I take a string like this and convert it such that the time is different?
This is would I'd expect:
const dateTimeString = '2017-11-14T16:04:54.0086709-06:00'
const newDateTimeString = (
moment(dateTimeString)
.changeTime('05:20 PM')
.format()
)
// newDateTimeString === '2017-11-14T17:20:00.0086709-06:00'

There is no built in function like changeTime, you can write your own using set.
You can add changeTime using moment.fn
The Moment prototype is exposed through moment.fn. If you want to add your own functions, that is where you would put them.
You can create a temp moment object with your "time to add" value using moment(String, String), then use set(Object(String, Int)) and getters like hours() and minutes().
Here a live sample:
moment.fn.changeTime = function(timeString) {
let m1 = moment(timeString, 'hh:mm A');
return this.set({h: m1.hours(), m: m1.minutes()});
}
const dateTimeString = '2017-11-14T16:04:54.0086709-06:00'
const newDateTimeString = (
moment(dateTimeString)
.changeTime('05:20 PM')
.format()
)
console.log(newDateTimeString);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.2/moment.min.js"></script>

If the user-entered time is formatted as such 13:00 you could do :
const dateTimeString = '2017-11-14T16:04:54.0086709-06:00'
var userInput = "13:20"
const newDateTimeString = (
moment(dateTimeString)
.hours(userInput.split(":")[0])
.minutes(userInput.split(":")[1])
.format()
)
Using https://momentjs.com/docs/#/get-set/hour/ and https://momentjs.com/docs/#/get-set/minute/
If it's formatted with PM and AM system, you could to the same, but with a little bit more of parsing, to know if it's 5.00 AM or PM.

One possible way is to use moment to grab the date and then combine it with your custom time value in another moment() call like so:
const newDateTimeString = (
moment(`${moment(dateTimeString).format('YYYY-MM-DD')} 05:20 PM`)
.format()
)

Relative Time jQuery Plugin (like Twitter, FB, etc) Breaks in Safari?

Works in all browsers except Firefox, any ideas?
(function($){
$.relativetime = function(options) {
var defaults = {
time:new Date(),
suffix:'ago',
prefix:''
};
options = $.extend(true, defaults, options);
//Fixes NaN in some browsers by removing dashes...
_dateStandardizer = function(dateString){
modded_date = options.time.toString().replace(/-/g,' ');
return new Date(modded_date)
}
//Time object with all the times that can be used throughout
//the plugin and for later extensions.
time = {
unmodified:options.time, //the original time put in
original:_dateStandardizer(options.time).getTime(), //time that was given in UNIX time
current:new Date().getTime(), //time right now
displayed:'' //what will be shown
}
//The difference in the unix timestamps
time.diff = time.current-time.original;
//Here we save a JSON object with all the different measurements
//of time. "week" is not yet in use.
time.segments = {
second:time.diff/1000,
minute:time.diff/1000/60,
hour:time.diff/1000/60/60,
day:time.diff/1000/60/60/24,
week:time.diff/1000/60/60/24/7,
month:time.diff/1000/60/60/24/30,
year:time.diff/1000/60/60/24/365
}
//Takes a string and adds the prefix and suffix options around it
_uffixWrap = function(str){
return options.prefix+' '+str+' '+options.suffix;
}
//Converts the time to a rounded int and adds an "s" if it's plural
_niceDisplayDate = function(str,date){
_roundedDate = Math.round(date);
s='';
if(_roundedDate !== 1){ s='s'; }
return _uffixWrap(_roundedDate+' '+str+s)
}
//Now we loop through all the times and find out which one is
//the right one. The time "days", "minutes", etc that gets
//shown is based on the JSON time.segments object's keys
for(x in time.segments){
if(time.segments[x] >= 1){
time.displayed = _niceDisplayDate(x,time.segments[x])
}
else{
break;
}
}
//If time.displayed is still blank (a bad date, future date, etc)
//just return the original, unmodified date.
if(time.displayed == ''){time.displayed = time.unmodified;}
//Give it to em!
return time.displayed;
};
})(jQuery);
In Safari, this code returns the given date which my plugin date if it fails. This could happen due to a future date or an invalid date. However, I'm not sure as the time that is given is standard YY MM DD HH:mm:ss
Demo:
http://jsfiddle.net/8azeT/

I think the string used is wrong and then stripped of '-' very wrong:
'010111' - interpreted by FF as Jan 1 1911 (US FF)
Correct format is '01/01/2011' (US FF)
I wouldn't use this format at all as each country has it's own way of showing/ parsing dates.
The safest way to parse a string is probably to use:
'January 1, 2011 1:30:11 pm GMT'
but I would use a date object instead in the options and skip the string parsing to make sure the date is correct.
http://jsfiddle.net/8azeT/4/
Question is about Safari but content FF?

Javascript DateFormat for different timezones

I'm a Java developer and I'm used to the SimpleDateFormat class that allows me to format any date to any format by settings a timezone.
Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
sdf.setTimeZone(TimeZone.getTimeZone("America/Los_Angeles"));
System.out.println(sdf.format(date)); // Prints date in Los Angeles
sdf.setTimeZone(TimeZone.getTimeZone("America/Chicago"));
System.out.println(sdf.format(date)); // Prints same date in Chicago
SimpleDateFormat is a pretty neat solution in Java but unfortunately I can't find any similar alternative in Javascript.
I'm extending the Date prototype in Javascript to do exactly the same. I have dates in Unix format but I want to format them in different timezones.
Date.prototype.format = function(format, timezone) {
// Now what?
return formattedDate;
}
I'm looking for a neat way to do this rather than a hack.
Thanks

There is a way to format for time zones.
console.log(new Date().toLocaleDateString('en-US', {timeZone: 'America/Denver'}))
// 11/13/2018
console.log(new Date().toLocaleTimeString('en-US', {timeZone: 'America/Denver'}))
// 2:30:54 PM
console.log(new Date().toLocaleTimeString('en-US', {timeZone: 'America/New_York'}))
// 4:31:26 PM
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleDateString
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleTimeString

The ISO Extended format for common date is YYYY-MM-DD, and for time is hh:mm:ss. Either format can be understood, unambiguously, worldwide.
See also:
http://jibbering.com/faq/#dates

If you're just passing the raw TZ there's nothing really complicated about adjusting the hours.
My example below is of course abbreviated. Yours may get quite long depending on how many patterns you'd handle.
Date.prototype.format = function(format, tzAdjust) {
// adjust timezone
this.setHours(this.getHours()+tzAdjust)
// pad zero helper - return "09" or "12"
var two = function(s){ return s+"".length==1 ? "0"+s : s+""; }
// replace patterns with date numbers
return format.replace(/dd|MM|yyyy|hh|mm|ss/g, function(pattern){
switch(pattern){
case "d" : return this.getDate();
case "dd" : return two(this.getDate());
}
});
}

Attempting to (ever so slightly) improve upon mwilcox's suggestion:
Date.prototype.format = function(format, tzAdjust) {
// get/setup a per-date-instance tzDate object store
var tzCache = this.__tzCache = this.__tzCache || (this.__tzCache = {});
// fetch pre-defined date from cache
var tzDate = tzCache[tzAdjust];
if ( !tzDate )
{
// on miss - then create a new tzDate and cache it
tzDate = tzCache[tzAdjust] = new Date( this );
// adjust by tzAdjust (assuming it's in minutes
// to handle those weird half-hour TZs :)
tzDate.setUTCMinutes( tzDate.getUTCMinutes()+tzAdjust );
}
return format.replace(/dd|MM|yyyy|hh|mm|ss/g, function(pattern){
// replace each format tokens with a value
// based on tzDate's corresponding UTC property
});
}

You are clearly asking two questions in one, formatting and time zone. They need to be addressed separately. Formatting is pretty trivial, if none of the other answers will do for that you will have to be more specific.
As for the time and time zone, if you have your server inject the UTC time, preferably as UNIX time in milliseconds, into the JavaScript, you can compare that to the time on the client machine, and thus work out how far from UTC the client is. Then you can calculate the time of any time zone you want.
Edit: I actually didn't know JavaScript also had built in UTC time until I checked on the internet, neat.
In any case, I suppose this is want you want:
Date.prototype.format=function(format,timezone){
var obj=new Date(this.getTime()+this.getTimezoneOffset()*60000+timezone*3600000);
var two=function(s){
return s<10?"0"+s:s+"";
}
return format.replace(/dd|MM|yyyy|hh|mm|ss/g, function(pattern){
switch(pattern){
case "dd" : return two(obj.getDate());
case "MM" : return two(obj.getMonth()+1);
case "yyyy" : return obj.getFullYear();
case "hh" : return two(obj.getHours());
case "mm" : return two(obj.getMinutes());
case "ss" : return two(obj.getSeconds());
}
});
}
You can add in more patterns if you need.

Don't write your own stuff; just get datejs: http://www.datejs.com/
You can figure out what the timezone offset is set to in the execution environment like this:
var local = new Date();
var utc = Date.UTC(local.getFullYear(), local.getMonth(), local.getDate(), local.getHours(), local.getMinutes(), local.getSeconds(), local.getMilliseconds());
var tz = (utc - local.getTime()) / (60 * 60 * 1000);

This is an old question, but since I found it:
As mentioned, there's nothing reasonable built-in.
As for libs, there is Moment Timezone for Moment.js.
Here is a JSfiddle with an example: http://jsfiddle.net/kunycrkb/
The same code inline:
var m = moment("2014-06-01T13:05:00Z");
var f = "HH:mm z";
$("#results").text(m.tz("UTC").format(f) + " is " + m.tz("EST").format(f) + "!");

Since my requirement was a typescript solution but I stumbled here I used this answer to write my typescript function.
Based on answer above, a function in typescript which converts a timestamp or a date object into a formatted local time string.
const formatDateString = (date_or_ts:Date|number):string=>{
let obj:Date;
if(typeof date_or_ts === "number"){
obj = new Date(date_or_ts*1000);
// obj=new Date(obj.getTime()+obj.getTimezoneOffset()*60000+timezone*3600000);
}else{
obj = date_or_ts;
}
const format = "dd-MM-yyyy hh:mm:ss";
let two=function(s:number){
return s<10?"0"+s:s+"";
}
return format.replace(/dd|MM|yyyy|hh|mm|ss/g, function(pattern){
const months = ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"];
switch(pattern){
case "dd" : return two(obj.getDate()).toString();
case "MM" : return months[obj.getMonth()];
case "yyyy" : return obj.getFullYear().toString();
case "hh" : return two(obj.getHours()).toString();
case "mm" : return two(obj.getMinutes()).toString();
case "ss" : return two(obj.getSeconds()).toString();
default: return "";
}
});
}