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Issues parsing a string-date React/JS

For example, I have this string "2020-09-09T21:00:14.114-04:00"
I grab this from my database and in its current form, it is a string. my goal is to have it display
4 PM instead of the long string of jibberish
is it possible to accomplish this?
I was thinking of possibly creating a new date object like
let test = new Date('2020-09-09T21:00:14.114-04:00').
but I'm stuck at the parsing and formatting part. it would be better to have this be done while the current state is a string but I don't think that this would be possible
edit: i would like the desired output to be the hour:minute and then am/pm
ex 10:15pm

You can do that by parsing the date from your database using Date.parse().
Then you can get the time or whatever you need using date.toLocalTimeString() in your case.
let dateUnix = Date.parse('2020-09-09T21:00:14.114-04:00');
const time = new Date(dateUnix).toLocaleTimeString();
console.log(time); // --> "4:00:14 AM"
The Date.parse() method parses a string representation of a date, and returns the number of milliseconds since January 1, 1970, 00:00:00 UTC or NaN if the string is unrecognized or, in some cases, contains illegal date values (e.g. 2015-02-31).
Here's some useful resources MDN Date.parse()
MDN Date.toLocalTimeString()

You can do as following way.new Date() is used to get the current date and time.
var today = new Date();
var time = today.getHours();
if(time>12){
var new_time= time % 12;
}
else{
var new_time= time;
}

How to obtain a local timezone Date from a date string in javascript?

I am building an online store, most of my customers (basically all) are located in a given timezone, but my infrastructure is located in other timezone (we can assume it's UTC). I have the option for my clients to select a date for their orders, the problem is that my date component represents dates like this "YYYY-MM-DD". In am using the Date constructor like this:
let dateString = "2019-06-03"
let date = new Date(dateString)
console.log(date) //This will print the local time zone representation of my dateString
console.log(date.toISOString()) //This will print the utc equivalent of my dateString
The problem with this is that I want the UTC representation to be calculated from the local timezone, not the other way around. Let's suppose in am located in GMT-5, when I say let date = new Date("2019-06-06") I want to see "2019-06-03T00:00:00.000 GMT-5" , and the ISOString should be "2019-06-03T05:00:00.000Z". How can I do this ?

What you are trying to achieve can be done by appending the string T00:00:00 to the dateString before passing it to the Date() constructor.
But a word of caution, manipulating the timezone/offsets manually like this might result in incorrect data being presented.
If you are storing and retrieving all the order timestamps in UTC only, it will avoid timezone related issues and you might not need to process the timestamps like this.
let dateString = "2019-06-03"
let date = new Date(dateString + "T00:00:00")
console.log(date) //This will print the local time zone representation of my dateString
console.log(date.toISOString()) //This will print the utc equivalent of my dateString

How to convert into Date time

When the date is passed from my c# to JavaScript it returns the date time as {4/3/2020 12:00:00 AM}
but in JavaScript it is shown as 1585852200000.
What is the format that is being used? And how can i convert it back?

You need to convert the Unix timestamp to DateTime format,
var localDate = new Date(1585852200000).toLocaleDateString("en-US")
console.log(localDate); // only local date
var localTime = new Date(1585852200000).toLocaleTimeString("en-US")
console.log(localTime) // only local time
// local datetime
console.log(new Date(1585852200000).toLocaleString());

1585852200000 is epoch date.
you can convert it as
var date = new Date(1585852200000)
console.log(new Date(1585852200000));

As an alternative from Shivaji's answer:
When you are passing the date through to JS you could cast it as a string with DateTime.ToString("dd/MM/yyyy") seen here on MSDN.
This will keep its integrity visually, if it is just for display purposes, otherwise you will need to re-cast appropriately in JS (in which case use Shivaji's answer).

JavaScript Date's object will return the DATE object and it's POSITION that is being assigned in your computer. So, when you are working with a date or datetime types, you can use some of the methods that are provided by the Date object, such as getDate() and getDay(). But, a better solution would be to format the Date object itself. For example: use the toString() or toUTCString() methods.
var d = new Date();
document.getElementById("demo").innerHTML = d.toString();
Reference:
https://www.w3schools.com/js/js_date_formats.asp
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date

Displaying timezone-formatted date as UTC time

on my UI, I try to display a date based on a specific timezone. In this example, I will use Americas/New_York as the timezone. This is how I did it.
$scope.getStartTime = function(){
var date = new Date();
return moment(date).tz("Americas/New_York").format('YYYY-MM-DD HH:mm:ss');
};
Afterwards, I want to send this data and send it to my server. In my server however, I want it so that it is always serialized into UTC time instead of in the New York Timezone (EST).
For example, if the time was 12:00 P.M. in New York, then the time would be serialized to 4:00 P.M. in UTC time before it was sent to the backend. This was my attempt:
var date = getStartTime();
....
// Display the date in the UI
....
$scope.revertStartTime(date);
$scope.revertStartTime = function(startTime) {
console.log("Start time: ", startTime);
console.log("Moment: ", moment(startTime).format());
console.log("Converted to utc time: ", moment().utc(startTime).format());
return moment.utc(startTime).format("YYYY-MM-DD'T'HH:mm:ss.SSSZ");
}
I tried to revert the start time by using the moment().utc() function and hoped that the date would change to a UTC based date but unfortunately it keeps turning my date into the localized date instead of UTC date and I'm not sure why. Any help would be appreciated. Thanks!
Edit:
Tried to follow the below method and here is what I did:
$scope.getStartTime = function(){
var date = new Date();
var startTime = new moment(date).tz($rootScope.userinfo.timeZone).format('YYYY-MM-DD HH:mm:ss');
$rootScope.offset = moment().utcOffset(startTime);
console.log("offset: ", $rootScope.offset);
return startTime;
};
$scope.revertStartTime = function(startTime) {
console.log("User Selected Time: ", moment().utcOffset(startTime).format('YYYY-MM-DD HH:mm:ss'));
return moment().utcOffset(startTime).format('YYYY-MM-DD HH:mm:ss');
}
But all I get is an error saying that revertStartTime returns an Invalid Date.

A few things:
Hoping it's a typo, but just to point out, the zone ID is America/New_York, not Americas/New_York.
You can pass a value as moment.utc(foo), or moment(foo).utc(), but not moment().utc(foo). The difference is that one interprets the input as UTC and stays in UTC mode, while they other just switches to UTC mode. You can also think of this as "converting to UTC", but really the underlying timestamp value doesn't change.
Yes, you can switch to UTC mode and call format, but you can also just call .toISOString() regardless of what mode you're in. That's already in the ISO format you're looking for.
Note that if you start with a unique point in time, and you end with converting to UTC, no amount of switching time zones or offsets in the middle will change the result. In other words, these are all equivalent:
moment().toISOString()
moment.utc().toISOString()
moment(new Date()).toISOString()
moment.utc(new Date()).toISOString()
moment(new Date()).utc().toISOString()
moment().tz('America/New_York').toISOString()
moment.tz('America/New_York').toISOString()
moment().utcOffset(1234).toISOString()
moment.utc().format('YYYY-MM-DD[T]HH:mm:ss.SSS[Z]')
moment().utc().format('YYYY-MM-DD[T]HH:mm:ss.SSS[Z]')
Only the last two even need to be in UTC mode, because the format function would produce different output if in local mode or in a particular time zone.

In order to accomplish this you'd want to use .utcOffset(). It is the preferred method as of Moment 2.9.0. This function uses the real offset from UTC, not the reverse offset (e.g., -240 for New York during DST). Offset strings like "+0400" work the same as before:
// always "2013-05-23 00:55"
moment(1369266934311).utcOffset(60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).utcOffset('+0100').format('YYYY-MM-DD HH:mm')
The older .zone() as a setter was deprecated in Moment.js 2.9.0. It accepted a string containing a timezone identifier (e.g., "-0400" or "-04:00" for -4 hours) or a number representing minutes behind UTC (e.g., 240 for New York during DST).
// always "2013-05-23 00:55"
moment(1369266934311).zone(-60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).zone('+0100').format('YYYY-MM-DD HH:mm')
To work with named timezones instead of numeric offsets, include Moment Timezone and use .tz() instead:
// determines the correct offset for America/Phoenix at the given moment
// always "2013-05-22 16:55"
moment(1369266934311).tz('America/Phoenix').format('YYYY-MM-DD HH:mm')

parsing a UTC ISO date to a local time date in javascript/jquery

I have tried to search for the answer already, and although I find answers that are very similar, I don't think they are exactly what I am looking for. Please forgive me if this is already answered elsewhere.
I am trying to parse an ISO date in javascript so that I can compare it to the client system date and display information depending on if the ISO date is before or after the client system date.
This was fine until I needed to support IE8 and now I am stuck.
I have created a function because I have three different dates that I need to do this to.
for example, my ISO date is: 2015-12-22T11:59 in UTC time.
but once my date is parsed, the full date is 11:59 in local time, no matter which time zone i test, it's always 11.59 in THAT time zone.
I know that the function I have created currently doesn't do anything with timezone, this is where I am stuck. I don't know what to add to get my end date to change as a reflection of the timezone of the clients machine.
any help or advice would be greatly appreciated.
I am not able to use something like moments.js because I have an upload restriction.
Jquery is available though. or plain javascript.
<script>
function setSaleContent() {
//creating a new date object that takes the clients current system time. so we can compare it to the dates stored in our array
var currentDate = new Date();
console.log(currentDate + " this is the clients date ");
//These variables actually come from an external array object, but I'm putting them in here like this for this example.
var destinations = {
freedate: "2015-12-16T11:59",
courierdate: "2015-12-22T11:59",
nextdaydate: "2015-12-23T11:59",
}
//fetch all the ISO dates from the array.
var freeDateISO = destinations["freedate"];
var courierDateISO = destinations["courierdate"];
var nextdayDateISO = destinations["nextdaydate"];
//I am creating this reusable function to split up my ISO date for the sake of IE8.. and create it into a date format that can be compared against another date. I know that this isn't doing anything with my timezone and that is where my problem lies.
function parseDate(str) {
var parts = /^(\d{4}).(\d{2}).(\d{2}).(\d{2}):(\d{2})/.exec(str);
if (parts) {
return new Date(parts[1], parts[2] - 1, parts[3], parts[4], parts[5]);
}
return new Date();
}
//I would like this date to change to reflect the time zone of the clients system time.
//currently returns the date at 11.59 regardless of timezone.
//If i was in GMT i would want it to say 11.59
//If i was in CT time I would like this to say 05.59
//If i was in Perth I would like this to say 19:59
var freeDate = parseDate(freeDateISO);
console.log(freeDate + " this is the converted date for IE")
}
window.onload = setSaleContent;

The simple solution is to append Z to the ISO date to indicate it is in UTC time, such as 2015-12-22T11:59Z.
When JavaScript parses that date as a string, it will then automatically convert the UTC date to the local time zone.
While this is simple enough with a parsing call in the form new Date(str);, it will not play nice with your parse call with numerical arguments targeting IE8 and other old browsers.
A polyfill for parsing ISO dates with timezone exists: Javascript JSON Date parse in IE7/IE8 returns NaN
This can replace your custom parseDate function after some modification to take an input string.
Alternatively, implement your own custom date manipulater to account for the local timezone using the .getTimezoneOffset() method on the newly created date, which gives the time zone offset in minutes, but you will have to come up with a method of utilising the offset such as adjusting hours and minutes, due to the limited methods of the JavaScript date object.