Develop Reference

How to handle date and time during conversion?

I'm trying to convert the time from AEST to IST. Not sure whether this approach is correct. My question with the below code is how can I deduct the date by 1 if the time shifts to the previous day?
The output should result : Thu Aug 24 2022 07:45:00
const date = 'August 25, 2022 12:15:00' // GMT+1000 (Australian Eastern Standard Time)" in 24 hours format
var IST = new Date(date);
IST.setHours(IST.getHours() - 5);
IST.setMinutes(IST.getMinutes() + 30);
console.log(IST.toString())

Javascript show next possible delivery date

I have a website, where the client can see the delivery date.
Here is the code
function getProductRecordHTML(Product, index, quantity, ProductType, blok)
{
var manufacturer = "", article_show = "", name = "";
var time_to_exe = Product.time_to_exe;
var displayDate;
if(time_to_exe == 6)
{
const date = new Date();
date.setDate(date.getDate() + parseInt(time_to_exe));
displayDate = date.toLocaleDateString();
}
if (displayDate) {
time_to_exe = displayDate;
} else {
time_to_exe = time_to_exe + "d";
}
For now, time_to_exe gives the delivery time in days
This code calculates the next delivery date just by adding these 6 days to the current date.
My main goal is to get the period from Monday to Wednesday at 12 pm, if it's true then time_to_exe shows the date of next Monday (for example 23/08/2021), but if it's false (for example it's period from Wednesday after 12 pm till Sunday 11:59 pm) then time_to_exe show Monday date 1-week after (for example 30/08/2021).
I hope explained clearly.
Already many thanks to the user #Christopher for helping before.

One way to work with dates much easier is to use a library like moment.js (which I have been using for years), or maybe even better a newer library like Luxon, since moment.js is going into maintenance mode.
Let's see how you would achieve your date calculation using moment.js:
var orderDateTime = moment('08/18/2021 8:15 am');
// Get Sunday (first day) of this week and add 3 days (to get to Wednesday) and set the time to 11:59am
var cutOffDate = moment().startOf('week').add(3,'days').set({'hour': 11, 'minute': 59, 'second': 59});
// Initialize delivery date from order date
var deliveryDate = orderDateTime.clone();
if (orderDateTime.isSameOrBefore(cutOffDate)) {
deliveryDate = deliveryDate.add(1,'week').startOf('week').add(1,'day'); // Monday next week
} else {
deliveryDate = deliveryDate.add(2,'week').startOf('week').add(1,'day'); // Monday the week after next
}
alert("Delivery Date is "+deliveryDate.format("MM/DD/YYYY"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>
That's all you need for your calculation.
You can also find a fiddle of the code above at https://jsfiddle.net/yLpf3vxj/

The Javascript Date object includes a getDay() method that returns a numerical value for the day of the week. From this it's possible to work out the previous Monday's date, and then add 7 or 14 depending on the original date.
This function takes a JavaScript Date object and returns the relevant Monday as another Date.
Note that setDate() will update month and year as appropriate if the date being set is outside the current month.
function getMonday(orderDate) {
orderDate = orderDate || new Date();
if (!(orderDate instanceof Date)) {
throw "Invalid date";
}
// Get the date last Monday
let lastMonday = new Date(orderDate);
lastMonday.setDate(lastMonday.getDate()-lastMonday.getDay()+1);
// If order date is before Wednesday noon, deliver next Monday. Add 7 to last Monday date
if (orderDate.getDay()<3 || ((orderDate.getDay() === 3) && orderDate.getHours()<12)) {
lastMonday.setDate(lastMonday.getDate()+7);
} else {
// Otherwise. add 14 to last Monday date.
lastMonday.setDate(lastMonday.getDate()+14);
}
return lastMonday;
}
input:
let testDates = [
new Date(),
new Date(2021,7,18,11),
new Date(2021,7,18,13),
new Date(2021,9,1,11),
'bad date'
];
Output:
Wed Aug 18 2021 10:14:41 GMT+1200 (New Zealand Standard Time), Mon Aug 23 2021 10:14:41 GMT+1200 (New Zealand Standard Time)
Wed Aug 18 2021 11:00:00 GMT+1200 (New Zealand Standard Time), Mon Aug 23 2021 11:00:00 GMT+1200 (New Zealand Standard Time)
Wed Aug 18 2021 13:00:00 GMT+1200 (New Zealand Standard Time), Mon Aug 30 2021 13:00:00 GMT+1200 (New Zealand Standard Time)
Fri Oct 01 2021 11:00:00 GMT+1300 (New Zealand Daylight Time), Mon Oct 11 2021 11:00:00 GMT+1300 (New Zealand Daylight Time)
Invalid Date
Demo:https://jsfiddle.net/dzsf34ga/

javascript Date.toISOString() return difference date value

I'm confusing about the javascript Date.toISOString() function which shown as below example, how come date value of x in ISO format become January?
const date = new Date();
const x = (new Date(date.getFullYear(), date.getMonth() , 1));
console.log(date); \\Tue Feb 04 2020 11:11:12 GMT+0800 (Malaysia Time)
console.log(x); \\Sat Feb 01 2020 00:00:00 GMT+0800 (Malaysia Time)
console.log(date.toISOString()); \\2020-02-04T03:11:12.330Z
console.log(x.toISOString()); \\2020-01-31T16:00:00.000Z

This is due to time zone conversion from GMT+08 to UTC. The toISOString function converts the date to UTC (as a note you can determine that the date is in the UTC time zone by "Z" at the end of the string).
When converting Feb 01 2020 00:00:00 GMT+0800 to an ISO string, the date is reduced by 8 hours and hence becomes Jan 31 2020 16:00:00.

If statement with date comparison

I'm trying to write an if statement that runs some code if the date is after April 24th, 2017, 10 am EDT, but it doesn't appear that my variables are comparable (different data types?).
I'm trying to avoid using Moment.js for just this.
var today = new Date();
var launch = 'Mon Apr 24 2017 10:00:00 GMT-0400 (EDT)';
today returns Tue Apr 04 2017 14:34:41 GMT-0400 (EDT).
When I test if either is greater than the other, both are false. How should I format my dates?
Thanks!

You have to have launch as a date type:
var today = new Date();
var launch = 'Mon Apr 24 2017 10:00:00 GMT-0400 (EDT)';
var launchDate = Date.parse(launch);
if ( launchDate > today )
You should also read more about dates here:
Compare two dates with JavaScript

How to set date always to eastern time regardless of user's time zone

I have a date given to me by a server in unix time: 1458619200000
NOTE: the other questions you have marked as "duplicate" don't show how to get there from UNIX TIME. I am looking for a specific example in javascript.
However, I find that depending on my timezone I'll have two different results:
d = new Date(1458619200000)
Mon Mar 21 2016 21:00:00 GMT-0700 (Pacific Daylight Time)
// Now I set my computer to Eastern Time and I get a different result.
d = new Date(1458619200000)
Tue Mar 22 2016 00:00:00 GMT-0400 (Eastern Daylight Time)
So how can I show the date: 1458619200000 ... to always be in eastern time (Mar 22) regardless of my computer's time zone?

You can easily take care of the timezone offset by using the getTimezoneOffset() function in Javascript. For example,
var dt = new Date(1458619200000);
console.log(dt); // Gives Tue Mar 22 2016 09:30:00 GMT+0530 (IST)
dt.setTime(dt.getTime()+dt.getTimezoneOffset()*60*1000);
console.log(dt); // Gives Tue Mar 22 2016 04:00:00 GMT+0530 (IST)
var offset = -300; //Timezone offset for EST in minutes.
var estDate = new Date(dt.getTime() + offset*60*1000);
console.log(estDate); //Gives Mon Mar 21 2016 23:00:00 GMT+0530 (IST)
Though, the locale string represented at the back will not change. The source of this answer is in this post. Hope this helps!

Moment.js (http://momentjs.com/timezone) is your friend.
You want to do something like this:
var d = new Date(1458619200000);
var myTimezone = "America/Toronto";
var myDatetimeFormat= "YYYY-MM-DD hh:mm:ss a z";
var myDatetimeString = moment(d).tz(myTimezone).format(myDatetimeFormat);
console.log(myDatetimeString); // gives me "2016-03-22 12:00:00 am EDT"

For daylight saving, Eastern time become 4 hours behind UTC. That's why its offset is -4x60 = -240 minutes. So when daylight is not active the offset will be -300. The offset variable's value is the key point to be noted here. Kindly see this code in action in attached image.
var offset = new Date().getTimezoneOffset();// getting offset to make time in gmt+0 zone (UTC) (for gmt+5 offset comes as -300 minutes)
var date = new Date();
date.setMinutes ( date.getMinutes() + offset);// date now in UTC time
var easternTimeOffset = -240; //for dayLight saving, Eastern time become 4 hours behind UTC thats why its offset is -4x60 = -240 minutes. So when Day light is not active the offset will be -300
date.setMinutes ( date.getMinutes() + easternTimeOffset);