Develop Reference

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/

How to convert a Date object to output only hh:mm am/pm

I am attempting to convert the following into a 12 hour am/pm format.
Currently I am recieving the Day, Month, Year and timezone.
Fixed by adding .toLocaleTimeString().replace(/([\d]+:[\d]{2})(:[\d]{2})(.)/, "$1$3")*
<div id="time1"></div>
<div id="time2"></div>
var date = new Date('08/16/2019 12:00:00 PM UTC').toLocaleTimeString().replace(/([\d]+:[\d]{2})(:[\d]{2})(.*)/, "$1$3")
document.getElementById("time1").innerHTML = date;
var date = new Date('08/16/2019 6:00:00 am UTC').toLocaleTimeString().replace(/([\d]+:[\d]{2})(:[\d]{2})(.*)/, "$1$3")
document.getElementById("time2").innerHTML = date;

Basically what you have to do is use the Date() default javascript function and make sure you append the UTC timezone:
var date = new Date('08/16/2019 7:00:00 PM UTC')
date.toString=() //will then print out the timezone adjusted time
"Fri Aug 16 2019 22:00:00 GMT+0300 (Eastern European Summer Time)"

There are many built in javascript methods to handle converting date objects. This example will look to the browser to determine date format and time.
let time = Date.now();
time.toLocaleDateString();

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);

Get timestamp with given date vs today date doesn't same result

Today is 18 Oct. 2013
var tmp = new Date('2013-10-18');
tmp = tmp.getTime();
1382054400000 (GMT: Fri, 18 Oct 2013 00:00:00 GMT)
var today = new Date();
today = today.setHours(0,0,0,0);
1382047200000 (GMT: Thu, 17 Oct 2013 22:00:00 GMT)
.setHours(0,0,0,0) Doesn't for set date to the midnight (00:00:00) ?

Date.setHours will set time to '00:00:00:00' in your current timezome.
Sets the hours for a specified date according to local time, and returns the number of milliseconds since 1 January 1970 00:00:00 UTC until the time represented by the updated Date instance.
If you want to work in UTC hours, use Date.setUTCHours instead.

getMonth getUTCMonth difference result

I found and inconsistent result when using the JavaScript date.getMonth() and date.getUTCMonth(), but only with some dates. The following example demonstrates the problem:
<!DOCTYPE html>
<html>
<body onload="myFunction()">
<p id="demo">Click the button to display the month</p>
<script type="text/javascript">
function myFunction()
{
var d = new Date(2012, 8, 1);
var x = document.getElementById("demo");
x.innerHTML=d;
x.innerHTML+='<br/>result: ' + d.getMonth();
x.innerHTML+='<br/>result UTC: ' + d.getUTCMonth();
}
</script>
</body>
</html>
The output of this example is:
Sat Sep 01 2012 00:00:00 GMT+0100 (Hora de Verão de GMT)
result: 8
result UTC: 7
If i change the date to (2012, 2, 1) the output is:
Thu Mar 01 2012 00:00:00 GMT+0000 (Hora padrão de GMT)
result: 2
result UTC: 2
In the first example, getMonth returns 7 and getUTCMonth returns 8. In the second example, both returns the same value 2.
Does anyone already experiences this situation? I am from Portugal and i think that it has something to be with my GMT but i don't understand why this is happening, because the examples are running in same circumstances.
Thanks in advances

You will see that, depending on YOUR TIMEZONE, the console logs may be different. I chose the first of the month '01' because it will be given a midnight default time '00:00:00', which will result in some timezones yielding February instead of March (you can get the full scoop here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse) :
let date1 = '2019-03-01'; // defaults to UTC
let date2 = '2019-03-01T14:48:00'; // LOCAL date/time
let dt1 = new Date(date1);
let dt2 = new Date(date2)
let month1 = dt1.getMonth();
let month2 = dt2.getMonth();
console.log("mon1: " + month1);
console.log("mon2: " + month2);

You will find that it is caused by DST difference.

Universal Time Zone date methods are used for working with UTC dates
Date returns month between 0 to 11
new Date(1976, 01 , 18) -
Wed Feb 18 1976 00:00:00 GMT+0530 (India Standard Time)
*getUTCDate return same as getDate() but returns Date based on World Time Zone, same with month and year
new Date(1976, 01 , 18).getUTCDate() -
17
new Date(1976, 01 , 18).getDate() -
18
new Date(1976, 02 , 18).getUTCMonth() -
2
new Date(1976, 01 , 18).getMonth() -
1
new Date(1976, 01 , 18).getYear() -
76
new Date(1976, 01 , 18).getUTCFullYear() -
1976
new Date(1976, 01 , 18).getFullYear() -
1976

A Date in js is just a timestamp, meaning there is no timezone information in any Date instance. A date is an absolute timed event (in opposition to a wall clock time which is relative to your timezone).
So… when you print the date to the console, because there is no timezone information in the date object, it will use your browser's timezone to format the date.
This is embarrassing because if you provide the same date to 2 clients, one in US and the other one in EU and ask them the date's month, because both are using their own timezone, you might end up with different answers.
To prevent this, getUTCMonth(); will use a default timezone of UTC (+0) instead of the client's browser so that the answer will be consistent whatever the client's timezone.