Develop Reference

get time different (minutes) in javascript

How do I calculate the difference in minutes given two strings. For example say I have
11:00
11:30
But of course the second string could be 12:11 so I can't subtract just the minutes.

first use javascript to convert the strings to time, then subtract, then convert back to strings
like this:
x = new Date("1/1/01 11:00")
y = new Date("1/1/01 11:30")
// now y-x has difference in milliseconds
// (y-x)/1000 is difference in seconds, etc
The data 1/1/01 is just being used as a dummy value, but the one thing you might have to worry about is are the times on different days, if so you will have to use 1/2/01 for the second time. Unless of course you always know the times are in the same day, but if they can cross "midnight" then you have to adjust for that.
You may want to use http://momentjs.com/ which will take care of the details for you.

When looking for getting metrics such as date , hour , minutes, seconds from the date difference, it's a lot easier to use basic notations as listed here
var x = new Date(new Date().getTime() + 11.5*60*60000); // adds 11 hours - 30 minutes
var y = new Date(new Date().getTime() + 11*60*60000); // adds 11 hours
alert(x.getMinutes() - y.getMinutes()); // gives the difference = 30
Here's an example : https://jsfiddle.net/DinoMyte/157knmgn/

Why does the following code not shift the current date forward by five days in JavaScript?

I am learning the Date class in JavaScript and am trying to move the current date forward by five days with the following code:
var today = new Date();
today = today.setDate(today.getDate() + 5);
However, when I run the code I get an extremely long number. Can anyone please explain what I am doing wrong?

This should be enough:
var today = new Date();
today.setDate(today.getDate() + 5);
... as you modify object stored in today anyway with setDate method.
However, with today = in place you assign the result of setDate call to today instead - and that's the number in milliseconds, according to docs:
Date.prototype.setDate(date)
[...]
4. Let u be TimeClip(UTC(newDate)).
5. Set the [[PrimitiveValue]] internal property of this Date object to u.
6. Return u.
Apparently, that number becomes a new value of today, replacing the object stored there before.

The setDate function updates your object with the correct time. You should do
var d = new Date()
d.setDate(d.getDate() + 5);
The d object will have the current date plus five days.
Another way is to use the setTime function. This function accepts as parameter the number of milliseconds since 1969 (the "Epoch" in UNIX time). Correspondingly, the getTime function returns the current date in milliseconds since the Epoch.
To add 5 days to the current date you need to add 5 * 24 * 3600 * 1000, that is, 5 times 24 hours (3600 seconds) times 1000.
var d = new Date()
d.setTime(d.getTime() + 5 * 24 * 3600 * 1000);
Note that your object will be updated and you don't need to watch for the return of neither setTime of setDate.

How to read the correct time/duration values from Google Spreadsheet

I'm trying to get from a time formatted Cell (hh:mm:ss) the hour value, the values can be bigger 24:00:00 for example 20000:00:00 should give 20000:
Table:
if your read the Value of E1:
var total = sheet.getRange("E1").getValue();
Logger.log(total);
The result is:
Sat Apr 12 07:09:21 GMT+00:09 1902
Now I've tried to convert it to a Date object and get the Unix time stamp of it:
var date = new Date(total);
var milsec = date.getTime();
Logger.log(Utilities.formatString("%11.6f",milsec));
var hours = milsec / 1000 / 60 / 60;
Logger.log(hours)
1374127872020.000000
381702.1866722222
The question is how to get the correct value of 20000 ?

Expanding on what Serge did, I wrote some functions that should be a bit easier to read and take into account timezone differences between the spreadsheet and the script.
function getValueAsSeconds(range) {
var value = range.getValue();
// Get the date value in the spreadsheet's timezone.
var spreadsheetTimezone = range.getSheet().getParent().getSpreadsheetTimeZone();
var dateString = Utilities.formatDate(value, spreadsheetTimezone,
'EEE, d MMM yyyy HH:mm:ss');
var date = new Date(dateString);
// Initialize the date of the epoch.
var epoch = new Date('Dec 30, 1899 00:00:00');
// Calculate the number of milliseconds between the epoch and the value.
var diff = date.getTime() - epoch.getTime();
// Convert the milliseconds to seconds and return.
return Math.round(diff / 1000);
}
function getValueAsMinutes(range) {
return getValueAsSeconds(range) / 60;
}
function getValueAsHours(range) {
return getValueAsMinutes(range) / 60;
}
You can use these functions like so:
var range = SpreadsheetApp.getActiveSheet().getRange('A1');
Logger.log(getValueAsHours(range));
Needless to say, this is a lot of work to get the number of hours from a range. Please star Issue 402 which is a feature request to have the ability to get the literal string value from a cell.

There are two new functions getDisplayValue() and getDisplayValues() that returns the datetime or anything exactly the way it looks to you on a Spreadsheet. Check out the documentation here

The value you see (Sat Apr 12 07:09:21 GMT+00:09 1902) is the equivalent date in Javascript standard time that is 20000 hours later than ref date.
you should simply remove the spreadsheet reference value from your result to get what you want.
This code does the trick :
function getHours(){
var sh = SpreadsheetApp.getActiveSpreadsheet();
var cellValue = sh.getRange('E1').getValue();
var eqDate = new Date(cellValue);// this is the date object corresponding to your cell value in JS standard
Logger.log('Cell Date in JS format '+eqDate)
Logger.log('ref date in JS '+new Date(0,0,0,0,0,0));
var testOnZero = eqDate.getTime();Logger.log('Use this with a cell value = 0 to check the value to use in the next line of code '+testOnZero);
var hours = (eqDate.getTime()+ 2.2091616E12 )/3600000 ; // getTime retrieves the value in milliseconds, 2.2091616E12 is the difference between javascript ref and spreadsheet ref.
Logger.log('Value in hours with offset correction : '+hours); // show result in hours (obtained by dividing by 3600000)
}
note : this code gets only hours , if your going to have minutes and/or seconds then it should be developped to handle that too... let us know if you need it.
EDIT : a word of explanation...
Spreadsheets use a reference date of 12/30/1899 while Javascript is using 01/01/1970, that means there is a difference of 25568 days between both references. All this assuming we use the same time zone in both systems. When we convert a date value in a spreadsheet to a javascript date object the GAS engine automatically adds the difference to keep consistency between dates.
In this case we don't want to know the real date of something but rather an absolute hours value, ie a "duration", so we need to remove the 25568 day offset. This is done using the getTime() method that returns milliseconds counted from the JS reference date, the only thing we have to know is the value in milliseconds of the spreadsheet reference date and substract this value from the actual date object. Then a bit of maths to get hours instead of milliseconds and we're done.
I know this seems a bit complicated and I'm not sure my attempt to explain will really clarify the question but it's always worth trying isn't it ?
Anyway the result is what we needed as long as (as stated in the comments) one adjust the offset value according to the time zone settings of the spreadsheet. It would of course be possible to let the script handle that automatically but it would have make the script more complex, not sure it's really necessary.

For simple spreadsheets you may be able to change your spreadsheet timezone to GMT without daylight saving and use this short conversion function:
function durationToSeconds(value) {
var timezoneName = SpreadsheetApp.getActive().getSpreadsheetTimeZone();
if (timezoneName != "Etc/GMT") {
throw new Error("Timezone must be GMT to handle time durations, found " + timezoneName);
}
return (Number(value) + 2209161600000) / 1000;
}
Eric Koleda's answer is in many ways more general. I wrote this while trying to understand how it handles the corner cases with the spreadsheet timezone, browser timezone and the timezone changes in 1900 in Alaska and Stockholm.

Make a cell somewhere with a duration value of "00:00:00". This cell will be used as a reference. Could be a hidden cell, or a cell in a different sheet with config values. E.g. as below:
then write a function with two parameters - 1) value you want to process, and 2) reference value of "00:00:00". E.g.:
function gethours(val, ref) {
let dv = new Date(val)
let dr = new Date(ref)
return (dv.getTime() - dr.getTime())/(1000*60*60)
}
Since whatever Sheets are doing with the Duration type is exactly the same for both, we can now convert them to Dates and subtract, which gives correct value. In the code example above I used .getTime() which gives number of milliseconds since Jan 1, 1970, ... .
If we tried to compute what is exactly happening to the value, and make corrections, code gets too complicated.
One caveat: if the number of hours is very large say 200,000:00:00 there is substantial fractional value showing up since days/years are not exactly 24hrs/365days (? speculating here). Specifically, 200000:00:00 gives 200,000.16 as a result.

Subtract two date variables and get in terms of days in javascript

Here is my code.
var today = new Date();
var reqDate = new Date(today.getFullYear(),today.getMonth()-3, today.getDate());
var day = today-reqDate;
I want the 'day' should be something around 90; but it gives as some long integer.

The long integer is the number of milliseconds since midnight Jan 1, 1970. So in order to get the number of days you need to divide it. Code below:
var days = day/(1000*60*60*24);

You have got value in day variable as milliseconds, so divide it by 1000*60*60*24 to get day count.
Another thing, it will be a decimal value.
So you have to discard fraction value using floor function.
var days = Math.floor(day/(1000*60*60*24));

How to perform date subtraction in javascript

It's a little complicated to calculate delta time in js.
this is the pseudo-code,
var atime = "2010-12-05T08:03:22Z";
var btime = "2010-01-11T08:01:57Z"
var delta_time = btime - atime;
delta_time ?
I want to know exact date time between two time inputs.
is there any easy way to find out delta time?

var atime = new Date("2010-12-05T08:03:22Z");
var btime = new Date("2010-01-11T08:01:57Z");
var delta_time = btime - atime;
The value of delta_time will be the difference between the two dates in milliseconds.
If you're only interested in the difference, and don't care to differentiate between which is the later date, you might want to do
var delta_time = Math.abs(btime - atime);

A Date / Time object displays a time in a current situation (e.g. now() ). Displaying a difference of time is not part of a Date or Time object because the difference between e.g. May 1 and May 3 would result in, maybe, January 3, 1970, or maybe May 2, depends on how you start counting your delta on.
I would suggest putting your times into a timestamp which is a simple int in seconds. Do some substraction and voilá, there's your delta seconds. This delta can be used to apply to any other Object.