Develop Reference

UTC live clock, not working with negative timezone

In my application, I need to create live clock according to different timezones which are stored into database.
I have almost succeeded it.
But now I'm facing negative time in clock, and I'm out of ideas to figure out a solution.
I'm getting UTC time with the help of new Date() and calculating time with provided timezone from database.
Case 1: 0:31 (UTC time) + 5:30 (timezone) = '06:01'
Case 2: 06:31 (UTC time) - 6:30 (timezone) = '00:01'
Case 3: 5:0 (UTC time) - 7:0 (timezone) = '-02:00'
Case 1 and 2 is working properly but I'm getting negative value in 3rd case which is wrong.
I have tried to add comments in code to have better understanding of what I'm doing here. I hope it helps.
Any help will be highly appreciated.
function runClock() {
setInterval(function() {
//debugger
var time = new Date();
// take timezone from HTML element
// ex: +:5:30
var getTimezone = "-:7:0" //$("#timeZone").text();
// split into array to get oparator (Positive and Negative Timezone)
var oparator = getTimezone.split(":")[0];
var timezone = getTimezone.split(":")[1] + ":" + getTimezone.split(":")[2];
// get UTC hours
var hours = 5 //time.getUTCHours();
var minutes = 0 //time.getUTCMinutes();
var UTCTIME = timeStringToFloat(hours + ":" + minutes);
var TIMEZONEOFFSETTIME = timeStringToFloat(timezone);
var finalTime = "";
// Convert time folloed by Colon into decimals
// ex: 1:45 = 1.75
function timeStringToFloat(time) {
var hoursMinutes = time.split(/[.:]/);
var hh = parseInt(hoursMinutes[0], 10);
var mm = hoursMinutes[1] ? parseInt(hoursMinutes[1], 10) : 0;
return hh + mm / 60;
}
// Convert time folloed by float into Colon
// ex: 1.75 = 1:45
function floatToTime(FT) {
var splittedTime = FT.toString().split(".");
var hh = splittedTime[0];
var mm = "";
if (splittedTime[1]) {
mm = Math.round((splittedTime[1] / 100) * 60);
} else {
mm = "0";
}
finalTime = hh + ":" + ((mm < 10) ? ("0" + mm) : mm);
}
// Calculate time (UTC + or - Timezone)
// Ex: 00:15 (UTC) + 5:30 = 5:45
function CalcTime(UTCTIME, TIMEZONEOFFSETTIME) {
if (oparator == "+") {
var FT = UTCTIME + TIMEZONEOFFSETTIME;
FT = FT.toFixed(2);
floatToTime(FT);
} else {
var FT = UTCTIME - TIMEZONEOFFSETTIME;
FT = FT.toFixed(2);
floatToTime(FT);
}
}
// Parse Seconds
function seconds() {
var j = "";
if (time.getUTCSeconds() < 10) {
j = "0" + time.getUTCSeconds();
} else {
j = time.getUTCSeconds()
}
return j;
}
CalcTime(UTCTIME, TIMEZONEOFFSETTIME);
$("#clockTime").text(finalTime + ":" + seconds());
}, 1000);
}
runClock();
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<b id="clockTime"></b>

You should just be "looping back" to 23:59 when you go negative. You can just add something to check if it goes negative then just re-add the missing time:
function CalcTime(UTCTIME, TIMEZONEOFFSETTIME) {
if (oparator == "+") {
var FT = UTCTIME + TIMEZONEOFFSETTIME;
FT = FT.toFixed(2);
floatToTime(FT);
} else {
var FT = UTCTIME - TIMEZONEOFFSETTIME;
// Offset any negative times;
if (FT < 0) {
FT += 24;
}
FT = FT.toFixed(2);
floatToTime(FT);
}
}
But ideally you really don't want to be handling these kinds of Timezone issues as other libraries are already handling it, i.e. moment.js
function runClock() {
setInterval(function() {
//debugger
var time = new Date();
// take timezone from HTML element
// ex: +:5:30
var getTimezone = "-:7:0" //$("#timeZone").text();
// split into array to get oparator (Positive and Negative Timezone)
var oparator = getTimezone.split(":")[0];
var timezone = getTimezone.split(":")[1] + ":" + getTimezone.split(":")[2];
// get UTC hours
var hours = 5 //time.getUTCHours();
var minutes = 0 //time.getUTCMinutes();
var UTCTIME = timeStringToFloat(hours + ":" + minutes);
var TIMEZONEOFFSETTIME = timeStringToFloat(timezone);
var finalTime = "";
// Convert time folloed by Colon into decimals
// ex: 1:45 = 1.75
function timeStringToFloat(time) {
var hoursMinutes = time.split(/[.:]/);
var hh = parseInt(hoursMinutes[0], 10);
var mm = hoursMinutes[1] ? parseInt(hoursMinutes[1], 10) : 0;
return hh + mm / 60;
}
// Convert time folloed by float into Colon
// ex: 1.75 = 1:45
function floatToTime(FT) {
var splittedTime = FT.toString().split(".");
var hh = splittedTime[0];
var mm = "";
if (splittedTime[1]) {
mm = Math.round((splittedTime[1] / 100) * 60);
} else {
mm = "0";
}
finalTime = hh + ":" + ((mm < 10) ? ("0" + mm) : mm);
}
// Calculate time (UTC + or - Timezone)
// Ex: 00:15 (UTC) + 5:30 = 5:45
function CalcTime(UTCTIME, TIMEZONEOFFSETTIME) {
if (oparator == "+") {
var FT = UTCTIME + TIMEZONEOFFSETTIME;
FT = FT.toFixed(2);
floatToTime(FT);
} else {
var FT = UTCTIME - TIMEZONEOFFSETTIME;
// Offset any negative times;
if (FT < 0) {
FT += 24;
}
FT = FT.toFixed(2);
floatToTime(FT);
}
}
// Parse Seconds
function seconds() {
var j = "";
if (time.getUTCSeconds() < 10) {
j = "0" + time.getUTCSeconds();
} else {
j = time.getUTCSeconds()
}
return j;
}
CalcTime(UTCTIME, TIMEZONEOFFSETTIME);
$("#clockTime").text(finalTime + ":" + seconds());
}, 1000);
}
runClock();
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<b id="clockTime"></b>

You want to recover/display the time for a given timezone offset? Unless you like doing this for a hobby, stay away from string methods and use the date functions, no?
var offsetMS = -5.5 * 3600000
var myDate = new Date()
var dateWithOffset = new Date( myDate.getTime() + offsetMS )
var formatted = dateWithOffset.toLocaleString("en-GB",{timeZone:"UTC",hour:"numeric",minute:"numeric"})
console.log(formatted)
Even manipulating timezone offset directly is to be avoided. If you can, use toLocaleString with a real timezone name, then issues like daylight saving will be handled for you. Modern browsers support all iana timezones, so let them do the work.

Add 24 to your FT value and take division remain of 24:
function CalcTime(UTCTIME, TIMEZONEOFFSETTIME) {
if (oparator == "+") {
var FT = UTCTIME + TIMEZONEOFFSETTIME;
} else {
var FT = UTCTIME - TIMEZONEOFFSETTIME + 24;
FT = FT % 24;
}
FT = FT.toFixed(2);
floatToTime(FT);
}
Working sample: https://codepen.io/anon/pen/VqQqoo

If you do not want to use a library like moment.js that comes with time zone handling and simply need to add/subtract hours from a given date, how about converting them to a common time unit and operating on that?
const timezoneString = '-:12:30';
const parts = timezoneString.split(':');
const timezone = (parts[0] === '-' ? -1 : 1) * (parseInt(parts[1]) + (parseInt(parts[2]) / 60.0));
const timeZoneMillis = timezone * 3600 * 1000;
const now = new Date();
const inZone = new Date(now.getTime() + timeZoneMillis);
console.log(now, inZone);
Something like this would convert them to a millisecond timestamp and subtract that many hours and convert it back to a date.

how to know the result of substraction of date

I have a date like this 2017-07-25 09:30:49, when I subtract 2017-07-25 10:30:00 and 2017-07-25 09:30:00, I need a result like 1 Hours.
I can't find correct search key for googling what I need.
Anyone know what should I search on google ? or someone knows some function about that?
PS. Mysql or Javascript

Try with date object in javascript
Like this
var d1 = new Date("2017-07-25 10:30:00");
var d2 = new Date("2017-07-25 09:30:49")
var diff = Math.abs(d1-d2); // difference in milliseconds
Then convert the milliseconds to hours
var hours = parseInt((diff/(1000*60*60))%24);

You can go through it
Get the time difference between two datetimes
But the query is not clear do you want only the hour difference or you want the difference converted to hour format
Like what it will give if 2017-07-25 09:30:49 and 2017-07-26 10:30:00 ? 25 hour or 1 hour?

here a code example of how to do it
var date1 = new Date("2017-07-25 09:30:49");
var date2 = new Date("2017-07-25 10:30:00");
var datesum = new Date(date1 - date2);
var hours = datesum.getHours();
var minutes = datesum.getMinutes();
var seconds = datesum.getSeconds();
console.log(hours + " hour, " + minutes + " minutes, " + seconds + " seconds" )

var dateString = "2017-07-25 09:30:49";
var dateString2= "2017-07-25 11:30:00";
var reggie = /(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/;
var dateArray = reggie.exec(dateString);
var dateArray2= reggie.exec(dateString2);
var dateObject1= new Date(
(+dateArray[1]),
(+dateArray[2])-1, // Careful, month starts at 0!
(+dateArray[3]),
(+dateArray[4]),
(+dateArray[5]),
(+dateArray[6])
);
var dateObject2= new Date(
(+dateArray2[1]),
(+dateArray2[2])-1, // Careful, month starts at 0!
(+dateArray2[3]),
(+dateArray2[4]),
(+dateArray2[5]),
(+dateArray2[6])
);
var diff = Math.abs(dateObject2-dateObject1); // difference in milliseconds
var hours = parseInt((diff/(1000*60*60))%24);

Try with the below dateFormatter function :
var d1 = new Date("2017-07-25 10:30:00");
var d2 = new Date("2017-07-25 09:30:00")
var diff = Math.abs(d1-d2);
var d = dateFormatter(diff);
console.log(d);
function dateFormatter(t){
var cd = 24 * 60 * 60 * 1000;
var ch = 60 * 60 * 1000;
var cm = 60*1000;
var d = Math.floor(t / cd);
var h = '0' + Math.floor( (t - d * cd) / ch);
var m = '0' + Math.round( (t - d * cd - h * ch) / 60000);
var s = '0' + Math.round((t - (d * cd) - (h * ch) - (m * cm))/1000);
return d + " days, " + h.substr(-2) + " hours, " + m.substr(-2) + " minutes, " +s.substr(-2)+ " seconds";
}

Convert javascript Date() to UTC and offset time

I have a countdown timer on a website (it acts as a same day shipment countdown timer, so the visitor knows if they place an order, it will be shipped out today if they're within the time window.) Basically the timer just counts down monday to friday until 5:00PM and then starts again at "0" (midnight, 24 hour clock) which was all working.
Then I realized that since the time is client side (javascript) visitors on the PST timezone will see a false time compared to what they should see (the store is Eastern).
Unfortunately I can't use php or anything server side to get the time from the server, so it has to be javascript (convert to UTC and offset).
I'm doing something wrong with the variables as far as I can tell, possibly more, could someone please tell me what I'm exactly setting wrong? (it doesn't show any errors in my console).
if (document.getElementById('countdownTimer')) {
pad = function(n, len) { // leading 0's
var s = n.toString();
return (new Array( (len - s.length + 1) ).join('0')) + s;
};
function calcTime(offset) {
// create Date object for current location
var d = new Date();
// convert to msec
// add local time zone offset
// get UTC time in msec
utc = d.getTime() + (d.getTimezoneOffset() * 60000);
offset = -5.0;
var now = utc + (3600000*offset);
function countDown() {
//var now = new Date();
if ( (now.getDay() >= 1) && (now.getDay() <= 5) ) { // Monday to Friday only
var target = 17; // 15:00hrs is the cut-off point
if (now.getHours() < target) { // don't do anything if we're past the cut-off point
var hrs = (target - 1) - now.getHours();
if (hrs < 0) hrs = 0;
var mins = 59 - now.getMinutes();
if (mins < 0) mins = 0;
var secs = 59 - now.getSeconds();
if (secs < 0) secs = 0;
var str = '<span id="day">00</span><span id="hour">' + pad(hrs, 2) + '</span><span id="minute">' + pad(mins, 2) + '</span><span id="second">' + pad(secs, 2) + '</span>';
document.getElementById('countdownTimer').innerHTML = str;
}
}
}
var timerRunning = setInterval('countDown()', 1000);
}
}

I see that in these lines :
// convert to msec
// add local time zone offset
// get UTC time in msec
utc = d.getTime() + (d.getTimezoneOffset() * 60000);
offset = -5.0;
var now = utc + (3600000*offset);
you're creating a now variable as a number, and then in your function countDown() you're using it as a date object.
You should create your now var as a date like this
var now = new Date(utc + (3600000*offset));

I just did this to set an expires header in node.js ... here's what I did:
res.setHeader("Expires", new Date(Date.now() + 345600000).toUTCString());
for another application you could do it differently:
var updated_date = new Date(Date.now() + 345600000, //miliseconds
utc_date = updated_date.toUTCString()
Have fun!

JavaScript date difference correction

I have a function that will calculate time between two date / time but I am having a small issue with the return.
Here is the way I collect the information.
Start Date
Start Time
Ending Date
Ending Time
Hours
And here is the function that calculates the dates and times:
function calculate (form) {
var d1 = document.getElementById("date1").value;
var d2 = document.getElementById("date2").value;
var t1 = document.getElementById("time1").value;
var t2 = document.getElementById("time2").value;
var dd1 = d1 + " " + t1;
var dd2 = d2 + " " + t2;
var date1 = new Date(dd1);
var date2 = new Date(dd2);
var sec = date2.getTime() - date1.getTime();
if (isNaN(sec)) {
alert("Input data is incorrect!");
return;
}
if (sec < 0) {
alert("The second date ocurred earlier than the first one!");
return;
}
var second = 1000,
minute = 60 * second,
hour = 60 * minute,
day = 24 * hour;
var hours = Math.floor(sec / hour);
sec -= hours * hour;
var minutes = Math.floor(sec / minute);
sec -= minutes * minute;
var seconds = Math.floor(sec / second);
var min = Math.floor((minutes * 100) / 60);
document.getElementById("result").value = hours + '.' + min;
}
If I put in todays date for both date fields and then 14:30 in the first time field and 15:35 in the second time field the result is shown as 1.8 and it should be 1.08
I didn't write this function but I am wondering if someone could tell me how to make that change?
Thank you.

If I understand correctly, the only issue you are having is that the minutes are not padded by zeroes. If this is the case, you can pad the value of min with zeroes using this little trick:
("00" + min).slice(-2)

I can't see why 15:35 - 14:30 = 1.08 is useful?
Try this instead:
function timediff( date1, date2 ) {
//Get 1 day in milliseconds
var one_day=1000*60*60*24;
// Convert both dates to milliseconds
var date1_ms = date1.getTime();
var date2_ms = date2.getTime();
// Calculate the difference in milliseconds
var difference_ms = date2_ms - date1_ms;
//take out milliseconds
difference_ms = difference_ms/1000;
var seconds = Math.floor(difference_ms % 60);
difference_ms = difference_ms/60;
var minutes = Math.floor(difference_ms % 60);
difference_ms = difference_ms/60;
var hours = Math.floor(difference_ms % 24);
var days = Math.floor(difference_ms/24);
return [days,hours,minutes,seconds];
}
function calculate (form) {
var d1 = document.getElementById("date1").value;
var d2 = document.getElementById("date2").value;
var t1 = document.getElementById("time1").value;
var t2 = document.getElementById("time2").value;
var dd1 = d1 + " " + t1;
var dd2 = d2 + " " + t2;
var date1 = new Date(dd1);
var date2 = new Date(dd2);
var diff = timediff(date1, date2);
document.getElementById("result").value = diff[1] + ':' + diff[2];
}

Verify if number of minutes is less than 10 and if it is then append an additional zero in front. Follow similar approach for seconds.

How to add hours to a Date object?

It amazes me that JavaScript's Date object does not implement an add function of any kind.
I simply want a function that can do this:
var now = Date.now();
var fourHoursLater = now.addHours(4);
function Date.prototype.addHours(h) {
// How do I implement this?
}
I would simply like some pointers in a direction.
Do I need to do string parsing?
Can I use setTime?
How about milliseconds?
Like this:
new Date(milliseconds + 4*3600*1000 /* 4 hours in ms */)?
This seems really hackish though - and does it even work?

JavaScript itself has terrible Date/Time API's. Nonetheless, you can do this in pure JavaScript:
Date.prototype.addHours = function(h) {
this.setTime(this.getTime() + (h*60*60*1000));
return this;
}

Date.prototype.addHours= function(h){
this.setHours(this.getHours()+h);
return this;
}
Test:
alert(new Date().addHours(4));

The below code will add 4 hours to a date (example, today's date):
var today = new Date();
today.setHours(today.getHours() + 4);
It will not cause an error if you try to add 4 to 23 (see the documentation):
If a parameter you specify is outside of the expected range, setHours() attempts to update the date information in the Date object accordingly

It is probably better to make the addHours method immutable by returning a copy of the Date object rather than mutating its parameter.
Date.prototype.addHours= function(h){
var copiedDate = new Date(this.getTime());
copiedDate.setHours(copiedDate.getHours()+h);
return copiedDate;
}
This way you can chain a bunch of method calls without worrying about state.

The version suggested by kennebec will fail when changing to or from DST, since it is the hour number that is set.
this.setUTCHours(this.getUTCHours()+h);
will add h hours to this independent of time system peculiarities.
Jason Harwig's method works as well.

Get a date exactly two hours from now, in one line.
You need to pass milliseconds to new Date.
let expiryDate = new Date(new Date().setHours(new Date().getHours() + 2));
or
let expiryDate2 = new Date(Date.now() + 2 * (60 * 60 * 1000) );
let nowDate = new Date();
let expiryDate = new Date(new Date().setHours(new Date().getHours() + 2));
let expiryDate2 = new Date(Date.now() + 2 * (60 * 60 * 1000) );
console.log('now', nowDate);
console.log('expiry', expiryDate);
console.log('expiry 2', expiryDate2);

You can use the Moment.js library.
var moment = require('moment');
foo = new moment(something).add(10, 'm').toDate();

I also think the original object should not be modified. So to save future manpower here's a combined solution based on Jason Harwig's and Tahir Hasan answers:
Date.prototype.addHours= function(h){
var copiedDate = new Date();
copiedDate.setTime(this.getTime() + (h*60*60*1000));
return copiedDate;
}

If you would like to do it in a more functional way (immutability) I would return a new date object instead of modifying the existing and I wouldn't alter the prototype but create a standalone function. Here is the example:
//JS
function addHoursToDate(date, hours) {
return new Date(new Date(date).setHours(date.getHours() + hours));
}
//TS
function addHoursToDate(date: Date, hours: number): Date {
return new Date(new Date(date).setHours(date.getHours() + hours));
}
let myDate = new Date();
console.log(myDate)
console.log(addHoursToDate(myDate,2))

There is an add in the Datejs library.
And here are the JavaScript date methods. kennebec wisely mentioned getHours() and setHours();

Check if it’s not already defined. Otherwise, define it in the Date prototype:
if (!Date.prototype.addHours) {
Date.prototype.addHours = function(h) {
this.setHours(this.getHours() + h);
return this;
};
}

This is an easy way to get an incremented or decremented data value.
const date = new Date()
const inc = 1000 * 60 * 60 // an hour
const dec = (1000 * 60 * 60) * -1 // an hour
const _date = new Date(date)
return new Date(_date.getTime() + inc)
return new Date(_date.getTime() + dec)

Another way to handle this is to convert the date to unixtime (epoch), then add the equivalent in (milli)seconds, then convert it back. This way you can handle day and month transitions, like adding 4 hours to 21, which should result in the next day, 01:00.

SPRBRN is correct. In order to account for the beginning/end of the month and year, you need to convert to Epoch and back.
Here's how you do that:
var milliseconds = 0; //amount of time from current date/time
var sec = 0; //(+): future
var min = 0; //(-): past
var hours = 2;
var days = 0;
var startDate = new Date(); //start date in local time (we'll use current time as an example)
var time = startDate.getTime(); //convert to milliseconds since epoch
//add time difference
var newTime = time + milliseconds + (1000*sec) + (1000*60*min) + (1000*60*60*hrs) + (1000*60*60*24*days);
var newDate = new Date(newTime); //convert back to date; in this example: 2 hours from right now
Or do it in one line (where variable names are the same as above:
var newDate =
new Date(startDate.getTime() + millisecond +
1000 * (sec + 60 * (min + 60 * (hours + 24 * days))));

For a simple add/subtract hour/minute function in JavaScript, try this:
function getTime (addHour, addMin){
addHour = (addHour ? addHour : 0);
addMin = (addMin ? addMin : 0);
var time = new Date(new Date().getTime());
var AM = true;
var ndble = 0;
var hours, newHour, overHour, newMin, overMin;
// Change form 24 to 12 hour clock
if(time.getHours() >= 13){
hours = time.getHours() - 12;
AM = (hours>=12 ? true : false);
}else{
hours = time.getHours();
AM = (hours>=12 ? false : true);
}
// Get the current minutes
var minutes = time.getMinutes();
// Set minute
if((minutes + addMin) >= 60 || (minutes + addMin) < 0){
overMin = (minutes + addMin) % 60;
overHour = Math.floor((minutes + addMin - Math.abs(overMin))/60);
if(overMin < 0){
overMin = overMin + 60;
overHour = overHour-Math.floor(overMin/60);
}
newMin = String((overMin<10 ? '0' : '') + overMin);
addHour = addHour + overHour;
}else{
newMin = minutes + addMin;
newMin = String((newMin<10 ? '0' : '') + newMin);
}
// Set hour
if((hours + addHour >= 13) || (hours + addHour <= 0)){
overHour = (hours + addHour) % 12;
ndble = Math.floor(Math.abs((hours + addHour)/12));
if(overHour <= 0){
newHour = overHour + 12;
if(overHour == 0){
ndble++;
}
}else{
if(overHour == 0){
newHour = 12;
ndble++;
}else{
ndble++;
newHour = overHour;
}
}
newHour = (newHour<10 ? '0' : '') + String(newHour);
AM = ((ndble + 1) % 2 === 0) ? AM : !AM;
}else{
AM = (hours + addHour == 12 ? !AM : AM);
newHour = String((Number(hours) + addHour < 10 ? '0': '') + (hours + addHour));
}
var am = (AM) ? 'AM' : 'PM';
return new Array(newHour, newMin, am);
};
This can be used without parameters to get the current time:
getTime();
Or with parameters to get the time with the added minutes/hours:
getTime(1, 30); // Adds 1.5 hours to current time
getTime(2); // Adds 2 hours to current time
getTime(0, 120); // Same as above
Even negative time works:
getTime(-1, -30); // Subtracts 1.5 hours from current time
This function returns an array of:
array([Hour], [Minute], [Meridian])

If you need it as a string, for example:
var defaultTime: new Date().getHours() + 1 + ":" + new Date().getMinutes();

I think this should do the trick
var nextHour = Date.now() + 1000 * 60 * 60;
console.log(nextHour)

You can even format the date in desired format using the moment function after adding 2 hours.
var time = moment(new Date(new Date().setHours(new Date().getHours() + 2))).format("YYYY-MM-DD");
console.log(time);

A little messy, but it works!
Given a date format like this: 2019-04-03T15:58
//Get the start date.
var start = $("#start_date").val();
//Split the date and time.
var startarray = start.split("T");
var date = startarray[0];
var time = startarray[1];
//Split the hours and minutes.
var timearray = time.split(":");
var hour = timearray[0];
var minute = timearray[1];
//Add an hour to the hour.
hour++;
//$("#end_date").val = start;
$("#end_date").val(""+date+"T"+hour+":"+minute+"");
Your output would be: 2019-04-03T16:58

The easiest way to do it is:
var d = new Date();
d = new Date(d.setHours(d.getHours() + 2));
It will add 2 hours to the current time.
The value of d = Sat Jan 30 2021 23:41:43 GMT+0500 (Pakistan Standard Time).
The value of d after adding 2 hours = Sun Jan 31 2021 01:41:43 GMT+0500 (Pakistan Standard Time).