Develop Reference

How to get current hour in milliseconds since epoch? [duplicate]

I am working on a project that requires a time in the future to be set using the Date object.
For example:
futureTime = new Date();
futureTime.setHours(futureTime.getHours()+2);
My questions is; once the future date is set, how can I round to the closest full hour and then set the futureTime var with it?
For example:
Given 8:55 => var futureTime = 9:00
Given 16:23 => var futureTime = 16:00
Any help would be appreciated!

Round the minutes and then clear the minutes:
var date = new Date(2011,1,1,4,55); // 4:55
roundMinutes(date); // 5:00
function roundMinutes(date) {
date.setHours(date.getHours() + Math.round(date.getMinutes()/60));
date.setMinutes(0, 0, 0); // Resets also seconds and milliseconds
return date;
}

The other answers ignore seconds and milliseconds components of the date.
The accepted answer has been updated to handle milliseconds, but it still does not handle daylight savings time properly.
I would do something like this:
function roundToHour(date) {
p = 60 * 60 * 1000; // milliseconds in an hour
return new Date(Math.round(date.getTime() / p ) * p);
}
var date = new Date(2011,1,1,4,55); // 4:55
roundToHour(date); // 5:00
date = new Date(2011,1,1,4,25); // 4:25
roundToHour(date); // 4:00

A slightly simpler way :
var d = new Date();
d.setMinutes (d.getMinutes() + 30);
d.setMinutes (0);

Another solution, which is no where near as graceful as IAbstractDownvoteFactory's
var d = new Date();
if(d.getMinutes() >= 30) {
d.setHours(d.getHours() + 1);
}
d.setMinutes(0);

Or you could mix the two for optimal size.
http://jsfiddle.net/HkEZ7/
function roundMinutes(date) {
return date.getMinutes() >= 30 ? date.getHours() + 1 : date.getHours();
}

As a matter of fact Javascript does this default which gives wrong time.
let dateutc="2022-02-17T07:20:00.000Z";
let bd = new Date(dateutc);
console.log(bd.getHours()); // gives me 8!!!!!
it is even wrong for my local time because I am GMT+2 so it should say 9.
moment.js also does it wrong so you need to be VERY carefull

Pass any cycle you want in milliseconds to get next cycle example 1 hours
function calculateNextCycle(interval) {
const timeStampCurrentOrOldDate = Date.now();
const timeStampStartOfDay = new Date().setHours(0, 0, 0, 0);
const timeDiff = timeStampCurrentOrOldDate - timeStampStartOfDay;
const mod = Math.ceil(timeDiff / interval);
return new Date(timeStampStartOfDay + (mod * interval));
}
console.log(calculateNextCycle(1 * 60 * 60 * 1000)); // 1 hours in milliseconds

How to convert hours:minutes using javascript

I am currently working on Jvascript datetime part in that getting NaN error while converting hours and minutes to seconds like strtotime in PHP so I want to know how to convert minutes and seconds like the way we do in strtotime in PHP.
var d = new Date();
var total = d.getHours() + ":" + d.getMinutes();
var ts = Date.parse(total);
document.write(ts);
In output getting error NaN

This is a sort of inane question, but here's the number of seconds in the hours and minutes of that number:
var d = new Date();
var total = (d.getHours() * 60 * 60) + (d.getMinutes() * 60);
document.write(total);

First of all, Date.parse() takes a string of a specific format (such as Jul 18, 2018). Second, it will not convert the date to seconds, but will return the number of milliseconds since January 1, 1970 00:00:00 GMT.
If you need to convert hh:mm to seconds, the correct approach is to multiply the value of getHours() by 3600 and multiply the value of getMinutes() by 60, then sum up the two values.
var d = new Date();
var timeinsecs = d.getHours() * 3600 + d.getMinutes() * 60;
document.write(timeinsecs);
While if you need to get the time in seconds from January 1, 1970 00:00:00 GMT till the current time, you will need to parse the current date then divide by 1000:
var d = new Date();
document.write(Date.parse(d) / 1000);

Just get hours and minutes, then sum them multiplying hours * 3600 and minutes * 60, like this
var d = new Date();
var total = d.getHours() * 3600 + d.getMinutes() * 60;
document.write(total)

If you want to follow your original approach of not doing the math by hand, you need to include a date before the time (any date should do, could be today if you wish) and convert ms to seconds (both of these for the reasons Wais Kamal pointed out) as follows.
var d = new Date();
var total = d.getHours() + ":" + d.getMinutes();
var someDate ='July 4, 1776';//works, but maybe safer to choose since 1990
total=someDate+', '+total;
var ts = Date.parse(total);
document.write((ts- Date.parse(someDate))/1000);

How to round down getTime result (ignoring minutes and hours)

I need to get the number of milliseconds of a certain day (even today), but need the result rounded down.
For example the number of milliseconds until this moment by using getTime() method is 1432738826994.
I would like to round this down to get the number of milliseconds until the beginning of the day, I need to get rid of all the minutes and hours. Is there a clean and simple way of achieving this?

If you are happy with using an external library, the easiest way is with moment.js.
moment().startOf('day').valueOf();
Will give you the unix epoch value for the beginning of today's date.
If you want to use the Javascript built in date object, then you would either need to set the hours, minutes, seconds and milliseconds to 0:
var rightNow = new Date();
rightNow.setHours(0);
rightNow.setMinutes(0);
rightNow.setSeconds(0);
rightNow.setMilliseconds(0);
Or create a new object from just the year, month and day values:
var rightNow = new Date();
var earlierToday = new Date(rightNow.getFullYear(), rightNow.getMonth(), rightNow.getDate(), 0, 0, 0, 0);

Pure javascript solution
var d = new Date();
var h = d.getHours();
var m = d.getMinutes();
var s = d.getSeconds();
var mi = d.getMilliseconds();
var fromStart = mi + (s * 1000) + (m * 60 * 1000) + (h * 60 * 60 * 1000);
var roundedDown = Date.now() - fromStart;
To print the start of the day use new Date(Date.now() - fromStart)

Why do I get +1 hour when calculating time difference in javascript?

I trying to create a very simple time difference calculation. Just "endtime - starttime". I'm getting +1 hour though. I suspect it has with my timezone to do, since I'm GMT+1.
Regardless, that should not affect the difference, since both start and end times are in the same timezone.
Check my running example-code here:
http://jsfiddle.net/kaze72/Rm3f3/
$(document).ready(function() {
var tid1 = (new Date).getTime();
$("#tid").click(function() {
var nu = (new Date).getTime();
var diff = new Date(nu - tid1);
console.log(diff.getUTCHours() + ":" +
diff.getUTCMinutes() + ":" +
diff.getUTCSeconds());
console.log(diff.toLocaleTimeString());
});
})

You must understand what Date object represent and how it stores dates. Basically each Date is a thin wrapper around the number of milliseconds since 1970 (so called epoch time). By subtracting one date from another you don't get a date: you just get the number of milliseconds between the two.
That being said this line doesn't have much sense:
var diff = new Date(nu - tid1);
What you really need is:
var diffMillis = nu - tid1;
...and then simply extract seconds, minutes, etc.:
var seconds = Math.floor(diffMillis / 1000);
var secondsPart = seconds % 60;
var minutes = Math.floor(seconds / 60);
var minutesPart = minutes % 60;
var hoursPart = Math.floor(minutes / 60);
//...
console.log(hoursPart + ":" + minutesPart + ":" + secondsPart);
Working fiddle.

Calculating time diference in JavaScript (days+hours+minutes+seconds)

lol sorry i posted it accidentally
I'm new to JavaScript and i'm trying to make a simple countdown script that should show the difference between the end date and today's server date.
here is a great example of what i'm trying to do http://moblog.bradleyit.com/2009/06/javascripting-to-find-difference.html
The only thing i want to add is another variable with a calculated seconds. How can i do that?
Here is the code:
var today = new Date();
var Christmas = new Date("12-25-2009");
var diffMs = (Christmas - today); // milliseconds between now & Christmas
var diffDays = Math.round(diffMs / 86400000); // days
var diffHrs = Math.round((diffMs % 86400000) / 3600000); // hours
var diffMins = Math.round(((diffMs % 86400000) % 3600000) / 60000); // minutes
alert(diffDays + " days, " + diffHrs + " hours, " + diffMins + " minutes until Christmas 2009 =)");

You have two issues with this code:
1: You need to use a date that will be accepted across browsers so it needs to be formatted with / instead of -.
2: You are rounding, which when rounding up will give you inaccurate numbers. All numbers need to be rounded down. Here is a function do do so:
var roundDown = function(num){
var full = num.toString();
var reg = /([\d]+)/i;
var res = reg.exec(full);
return res[1];
}
So your final code should look like this:
var roundDown = function(num){
var full = num.toString();
var reg = /([\d]+)/i;
var res = reg.exec(full);
return res[1];
}
var today = new Date(); // date and time right now
var goLive = new Date("06/01/2013"); // target date
var diffMs = (goLive - today); // milliseconds between now & target date
var diffDays = roundDown(diffMs / 86400000); // days
var diffHrs = roundDown((diffMs % 86400000) / 3600000); // hours
var diffMins = roundDown(((diffMs % 86400000) % 3600000) / 60000); // minutes
var diffSecs = roundDown((((diffMs % 86400000) % 3600000) % 60000) / 1000 ); // seconds

var endDate = new Date(year, month, day, hours, minutes, seconds, milliseconds);
var today = Date.now()
var timeLeft = endDate - today // timeLeft would be in milliseconds
// Parse this into months, days, hours, ...
Put this in a function and set it up to be called every second or so using setInterval.

This should get you started with the JavaScript date object and it's associated methods.
http://www.w3schools.com/jsref/jsref_obj_date.asp
Also, look up the setInterval() method, that will allow you to fire code in set intervals (for example, updating the countdown text).