As the title says I'm trying to get the first day name that a given month starts on. So for example if Oct 2014 was given the code would return 3 because there are 3 empty blocks before Wed the 1st. Again if I provided Jan 2015, I should get 4. Here is my function:
function getDayMonthStartsOn(month, year) {
var day = new Date(year + "-" + month + "-01").getDay();
day = (day === 0) ? 7 : day;
return day;
}
My problem is that it seems to work for Jan 2015 but not Oct 2014.
Use getUTCDay() instead of getDay().
Related
Cut Off Date: the cut off date is set as the coming bimonthly Friday (eg cut off dates are Jun 14 and Jun 28. If the submission is done today(June26th), then cut off date is Jun 28. If the submission is done on Jun 29th, the cut off date would be Jul 12. Once it's July 13th the next cutoffdate would be July 26th. And so on, depending on when the user submits the form it will display the correct cutoffdate. I've looked around at a few other examples, but can't find one for what I want.
var currentDate = new Date(new Date().getTime())
document.getElementById('lastsubmission').value =
(currentDate.getDate()) + '/' + (currentDate.getMonth() + 1) + '/' +
currentDate.getFullYear() + '#' + currentDate.getHours() + ':' +
currentDate.getMinutes() + ':' + currentDate.getSeconds();
You seem to want to get the next Friday after a date that is either the second or fourth Fridays of a month. Something like:
Get the second Friday of the date's month
If it's before that, return the second Friday
If it's after then, get the fourth Friday of the month
If it's before then, return the fourth Friday
If it's after then, return the second Friday of next month
So you might need a function to get a particular Friday given a date, and some other code to do the rest of the logic, e.g.
// Given a Date, return the nth Friday of that month
function getNthFriday(date, n) {
// Get first Friday
let d = new Date(date);
d.setDate(1);
let day = d.getDay();
d.setDate(d.getDate() + 5 - (day > 5? -1 : day));
// Set to nth Friday
d.setDate(d.getDate() + (n-1)*7);
return d;
}
// Return the next Friday after date that is either the
// second or fourth Friday's of a month.
function getCutoffDate(date) {
// Get 2nd Friday
var friday = getNthFriday(date, 2);
// If before, return 2nd Friday
if (date < friday) {
return friday;
}
// Get 4th Friday
friday = getNthFriday(date, 4);
// If before, return 4th Friday
if (date < friday) {
return friday;
}
// Otherwise, return 2nd Friday of next month
friday = getNthFriday(new Date(date.getFullYear(), date.getMonth()+1, 1), 2);
return friday;
}
// Some tests
[
new Date(2019,4,30), // 30 May 2019 -> 14 Jun
new Date(2019,5, 1), // 2 Jun 2019 -> 14 Jun
new Date(2019,5,13), // 13 Jun 2019 -> 28 Jun
new Date(2019,5,23), // 23 Jun 2019 -> 14 Jun
new Date(2019,5,30) // 30 Jun 2019 -> 12 Jul
].forEach(d => {
console.log(getCutoffDate(d).toString());
});
A library might help with getting the nth Friday, and getting the first day of the next month.
For a project app I'm making, a homework keeper, I need to be able to turn a number like 10 into a month like october, then do this with year, month, day, and time. Then I need to save it all in a date. How do I do this? I have been looking everywhere and cannot find how to do it.
It looks like you're looking for the Date() constructor.
var month = 10;
var day = 17;
var year = 2017;
var hour = 8;//Use the 24 hour clock for times in the PM
var minutes = 36;
var date = new Date(year, month-1, day, hour, minutes);//Outputs October 17th, 2017 at 8:36am in your local timezone
You have to subtract 1 from the month because January starts at 0, not 1.
Alternatively, I like to use moment.js for the flexibility depending on use, so you could instantiate it like this:
var date = moment(year + '-' + month + '-' + day + ' ' + hour + ':' + minutes, 'YYYY-M-D H:m');//Because you are using numbers/integers, none of them will have preceding zeroes
Take a look at the Date constructor - I think it doesn everything you need.
Your biggest gotcha is that months are 0-indexed so you'll actually turn 9 into October. Also beware that if you don't initialise Date with anything, it'll assume you mean now.
var date = new Date();
date; // -> Tue Oct 17 2017 13:34:49 GMT+0100 (GMT Daylight Time)
date.setMonth(10); // -> 1510925689970
date; // -> Fri Nov 17 2017 13:34:49 GMT+0000 (GMT Standard Time)
I'm trying to subtract one month from 2015-12-31 but it gives me 2015-12-01 instead of 2015-11-30. Why ?
Code:
var date1 = new Date('2015-12-31');
var date2 = new Date(date1);
date2.setMonth(date1.getMonth() - 1);
console.log(date1);
console.log(date2);
Output:
Thu Dec 31 2015 01:00:00 GMT+0100 (CET)
Tue Dec 01 2015 01:00:00 GMT+0100 (CET)
Any workaround?
When subtracting months, you can check whether the day of the adjusted Date is different to the day of the initial Date. If it is, then it must have rolled over to the next month, so set the day of the adjusted Date to 0, so it goes to the last day of the previous month, e.g.
function subtractMonths(date, months) {
var day = date.getDate();
date.setMonth(date.getMonth() - months);
if (date.getDate() != day) date.setDate(0);
return date;
}
// 31 Mar 2016 - 1 month = 29 Feb 2015
[[new Date(2016,2,31), 1],
// 29 Feb 2016 - 12 months = 28 Feb 2015
[new Date(2016,1,29), 12],
// 15 Feb 2016 - 3 months = 15 Nov 2015
[new Date(2016,1,15), 3]].forEach(function(arr){
document.write('<br>' + subtractMonths(arr[0], arr[1]));
})
The same algorithm can be used for adding months. Note that this is why date arithmetic is not symmetric, e.g.
31 May + 1 month => 30 June
30 June - 1 month => 30 May
i.e. If A + B = C, then C - B = A may or may not be true (and vice versa).
Try this
var date1 = new Date('2015-12-31');
var date2 = new Date(date1);
date2.setDate(date2.getDate()-date1.getDate());
alert(date2)
Per the setMonth documentation, ‘If you do not specify the [optional] dayValue parameter, the value returned from the getDate() method is used’. Since you’re not specifying the optional parameter, your code tries to set the date to 2015-11-31, which isn’t valid. JavaScript resolves this situation by setting the date to one day after 2015-11-30, which is 2015-12-01.
As for a workaround, it depends on what you’re actually trying to do. Are you trying to go 31 days back from 31 December? Or are you trying to get the last day of the month before December? Date semantics are extremely complicated; what are you going to do when the inevitable edge cases arise?
It is producing the requested result, which is subtracting 1 month from the date given. But remember a month is a variable amount of time. November 31 is actually December 1 (just like November 55th would actually be December 25, Christmas). To get the last day of the previous month you could do something like this:
var date = new Date('2015-12-31');
date.setDate(-1)
1) Oracle's example of ADD_MONTHS(date, 1):
SELECT ADD_MONTHS('30-Nov-15', 3) FROM dual;
February, 29 2016 00:00:00
2) JavaScript:
var date= new Date("Mon Nov 30 2015 00:00:00");
date.setMonth(date.getMonth() + 3);
Tue Mar 01 2016 00:00:00
Are there any JavaScript methods that can replicate the Oracle's ADD_MONTH() functionality ?
If you want to implement the same logik as in Oracle function - i.e. for "shorter" month you do not overflow in the next month, I guess you will need to do it yourself:
Pseudocode:
myDay = date.getDate(); // save the date
date.setMonth(date.getMonth() + 3); // add months
myNewDay = date.getDate();
while (myDay != myNewDay & myNewDay <= 3) {
myNewDay = myNewDay -1 // go back one day
date.setDate(myNewDay); // restore the
}
So if you end with the same day of the month after adding months you are ready.
If you get a different day of month, it will be 1,2 or 3 (the difference in month length);
go back day by day until you reach the end of the month.
This is my knowledge of the Oracle algorithm. HTH.
date.getMonth()
returns the previous months date instead of this months date. So to add to the correct date just do
date.setMonth(date.getMonth() + 2);
This question already has answers here:
How to get first and last day of the current week in JavaScript
(32 answers)
Closed 7 years ago.
I was using a function to return me the start and end day of a given week number from the year. Here is the function:
function getWeekRange(week){
var d = new Date("Jan 01, " + $scope.today.getFullYear() + " 01:00:00");
var w = d.getTime() + 604800000 * (week);
var d1 = new Date(w);
var d2 = new Date(w + 518400000);
return {
startDate: d1,
endDate: d2,
};
}
I set the year dynamically, and let's see an example where the year is 2015. Considering the week number starting by 0, if I use getWeekRange(0) I will receive the following result:
{
startDate: Thu Jan 01 2015 01:00:00 GMT-0200 (BRST),
endDate: Wed Jan 07 2015 01:00:00 GMT-0200 (BRST)
}
The problem is that this code does not consider the year of 2015 starting on a Thursday. The correct result for getWeekRange(0) should be:
{
startDate: Thu Jan 01 2015 01:00:00 GMT-0200 (BRST),
endDate: Sat Jan 03 2015 01:00:00 GMT-0200 (BRST)
}
and the result for getWeekRange(1) should be:
{
startDate: Sun Jan 04 2015 01:00:00 GMT-0200 (BRST),
endDate: Sat Jan 10 2015 01:00:00 GMT-0200 (BRST)
}
Does anyone have a clue?
-- EDIT --
My question is different from this one, because I don't have a given day of the year, I have only a week number of the year (from 0 to 51), and my case considers that the first week of the year is only a part of a full week, as mentioned by likeitlikeit.
I could find a simple solution for my question, since only the first week of my year could cause me problems. Here is the code:
function getWeekRange(week){
var d = new Date("Jan 01, " + $scope.today.getFullYear() + " 01:00:00");
var firstWeekDays = 7 - d.getDay();
var d1, d2;
if(week > 0) {
var w = d.getTime() + 604800000 * (week-1) + 24*60*60*1000 * firstWeekDays;
d1 = new Date(w);
d2 = new Date(w + 518400000);
} else {
d1 = d;
d2 = new Date(d1.getTime() + 24*60*60*1000 * (6 - d1.getDay()));
}
return {
startDate: d1,
endDate: d2,
};
}
There are 2 main diferences from the initial code.
For the week of the year I simply get the initial day of the year, and then based on the day of the week it starts I can find the end day of the week
For the other weeks, I sum 7*week-1 days to initial day (this sum does not consider the number of days of the first week), and also add firstWeekDays which is the number of days of first week (because it is not always 7 as the other weeks).
If anyone has a better solution, I will be glad to listen.
This answer shows how to get the first day of a week using getDate to calculate the offset from the current day.
Using this method, you can use getDate to determine which day of the week the first day of the year falls on. You can then subtract the last day of the week from this value to know how many days to add to your d2 in order to compute the date for Saturday by adjusting your date from the first day of the year + the offset in days till the end of the week for Jan 1.