How can I show the days of last week in javascript?

How can I show the days of last week in javascript? - javascript

I need a script that show the days of the last week, until today.
But when it's early in the month, like on day 4, my code has this problem.
I'm using getDate(). Is there a function that can help me?
result

You can use getDate(), but don't put it in a variable that you then just decrement with the risk of going to 0 and below.
Instead use setDate() (potentially in combination with getDate()) to decrement your date object day by day, and then read out the date in the format you want:
var dt = new Date();
headers = ['Hoje'];
for (var i = 1; i < 7; i++) {
dt.setDate(dt.getDate() - 1);
headers.push(dt.toLocaleDateString('pt-PT').substr(0,5));
}
console.log(headers);

To go back a week from today, regardless of where in the month you are (even within seven days from the beginning of the month), just .setDate() to a value that is seven (days) less than what .getDate() gives:
var d = new Date()
d.toDateString()
"Thu May 04 2017"
// go back a week
d.setDate(d.getDate() - 7);
1493321406767
// prove that it worked
d.toDateString()
"Thu Apr 27 2017"

You can use getDay method which gives the day of the week (1-monday, 3-wednesday). From this value you can put a decreasing loop till 1-monday or 0-sunday to show previous day of week.
var weekdays = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"];
var d = new Date();
var currDay = d.getDay();
var currDate = d.getDate();
var str = "";
for(var count=currDay; count>=0 && currDate >= 1; count--, currDate--){
str += currDate +" "+weekdays[count] + ", ";
}
console.log(str);
Today's output: 5 Fri, 4 Thu, 3 Wed, 2 Tue, 1 Mon

Related

End of Month using javascript [duplicate]

If you provide 0 as the dayValue in Date.setFullYear you get the last day of the previous month:
d = new Date(); d.setFullYear(2008, 11, 0); // Sun Nov 30 2008
There is reference to this behaviour at mozilla. Is this a reliable cross-browser feature or should I look at alternative methods?

var month = 0; // January
var d = new Date(2008, month + 1, 0);
console.log(d.toString()); // last day in January
IE 6: Thu Jan 31 00:00:00 CST 2008
IE 7: Thu Jan 31 00:00:00 CST 2008
IE 8: Beta 2: Thu Jan 31 00:00:00 CST 2008
Opera 8.54: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.27: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.60: Thu Jan 31 2008 00:00:00 GMT-0600
Firefox 2.0.0.17: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Firefox 3.0.3: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Google Chrome 0.2.149.30: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Safari for Windows 3.1.2: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Output differences are due to differences in the toString() implementation, not because the dates are different.
Of course, just because the browsers identified above use 0 as the last day of the previous month does not mean they will continue to do so, or that browsers not listed will do so, but it lends credibility to the belief that it should work the same way in every browser.

I find this to be the best solution for me. Let the Date object calculate it for you.
var today = new Date();
var lastDayOfMonth = new Date(today.getFullYear(), today.getMonth()+1, 0);
Setting day parameter to 0 means one day less than first day of the month which is last day of the previous month.

I would use an intermediate date with the first day of the next month, and return the date from the previous day:
int_d = new Date(2008, 11+1,1);
d = new Date(int_d - 1);

In computer terms, new Date() and regular expression solutions are slow! If you want a super-fast (and super-cryptic) one-liner, try this one (assuming m is in Jan=1 format). I keep trying different code changes to get the best performance.
My current fastest version:
After looking at this related question Leap year check using bitwise operators (amazing speed) and discovering what the 25 & 15 magic number represented, I have come up with this optimized hybrid of answers (note the parameters m & y must obviously be integers for this to work):
function getDaysInMonth(m, y) {
return m===2 ? y & 3 || !(y%25) && y & 15 ? 28 : 29 : 30 + (m+(m>>3)&1);
}
Given the bit-shifting this obviously assumes that your m & y parameters are both integers, as passing numbers as strings would result in weird results.
JSFiddle: http://jsfiddle.net/TrueBlueAussie/H89X3/22/
JSPerf results: http://jsperf.com/days-in-month-head-to-head/5
For some reason, (m+(m>>3)&1) is more efficient than (5546>>m&1) on almost all browsers.
The only real competition for speed is from #GitaarLab, so I have created a head-to-head JSPerf for us to test on: http://jsperf.com/days-in-month-head-to-head/5
It works based on my leap year answer here: javascript to find leap year this answer here Leap year check using bitwise operators (amazing speed) as well as the following binary logic.
A quick lesson in binary months:
If you interpret the index of the desired months (Jan = 1) in binary you will notice that months with 31 days either have bit 3 clear and bit 0 set, or bit 3 set and bit 0 clear.
Jan = 1 = 0001 : 31 days
Feb = 2 = 0010
Mar = 3 = 0011 : 31 days
Apr = 4 = 0100
May = 5 = 0101 : 31 days
Jun = 6 = 0110
Jul = 7 = 0111 : 31 days
Aug = 8 = 1000 : 31 days
Sep = 9 = 1001
Oct = 10 = 1010 : 31 days
Nov = 11 = 1011
Dec = 12 = 1100 : 31 days
That means you can shift the value 3 places with >> 3, XOR the bits with the original ^ m and see if the result is 1 or 0 in bit position 0 using & 1. Note: It turns out + is slightly faster than XOR (^) and (m >> 3) + m gives the same result in bit 0.
JSPerf results: http://jsperf.com/days-in-month-perf-test/6

My colleague stumbled upon the following which may be an easier solution
function daysInMonth(iMonth, iYear)
{
return 32 - new Date(iYear, iMonth, 32).getDate();
}
stolen from http://snippets.dzone.com/posts/show/2099

A slight modification to solution provided by lebreeze:
function daysInMonth(iMonth, iYear)
{
return new Date(iYear, iMonth, 0).getDate();
}

I recently had to do something similar, this is what I came up with:
/**
* Returns a date set to the begining of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function beginningOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1)
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
return date;
}
/**
* Returns a date set to the end of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function endOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1); // Avoids edge cases on the 31st day of some months
date.setMonth(date.getMonth() +1);
date.setDate(0);
date.setHours(23);
date.setMinutes(59);
date.setSeconds(59);
return date;
}
Pass it in a date, and it will return a date set to either the beginning of the month, or the end of the month.
The begninngOfMonth function is fairly self-explanatory, but what's going in in the endOfMonth function is that I'm incrementing the month to the next month, and then using setDate(0) to roll back the day to the last day of the previous month which is a part of the setDate spec:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/setDate
https://www.w3schools.com/jsref/jsref_setdate.asp
I then set the hour/minutes/seconds to the end of the day, so that if you're using some kind of API that is expecting a date range you'll be able to capture the entirety of that last day. That part might go beyond what the original post is asking for but it could help someone else looking for a similar solution.
Edit: You can also go the extra mile and set milliseconds with setMilliseconds() if you want to be extra precise.

How NOT to do it
Beware of any answers for the last of the month that look like this:
var last = new Date(date)
last.setMonth(last.getMonth() + 1) // This is the wrong way to do it.
last.setDate(0)
This works for most dates, but fails if date is already the last day of the month, on a month that has more days than the following month.
Example:
Suppose date is 07/31/21.
Then last.setMonth(last.getMonth() + 1) increments the month, but keeps the day set at 31.
You get a Date object for 08/31/21,
which is actually 09/01/21.
So then last.setDate(0) results in 08/31/21 when what we really wanted was 07/31/21.

try this one.
lastDateofTheMonth = new Date(year, month, 0)
example:
new Date(2012, 8, 0)
output:
Date {Fri Aug 31 2012 00:00:00 GMT+0900 (Tokyo Standard Time)}

This works for me.
Will provide last day of given year and month:
var d = new Date(2012,02,0);
var n = d.getDate();
alert(n);

This one works nicely:
Date.prototype.setToLastDateInMonth = function () {
this.setDate(1);
this.setMonth(this.getMonth() + 1);
this.setDate(this.getDate() - 1);
return this;
}

You can get the First and Last Date in the current month by following the code:
var dateNow = new Date();
var firstDate = new Date(dateNow.getFullYear(), dateNow.getMonth(), 1);
var lastDate = new Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0);
or if you want to format the date in your custom format then you can use moment js
var dateNow= new Date();
var firstDate=moment(new Date(dateNow.getFullYear(),dateNow.getMonth(), 1)).format("DD-MM-YYYY");
var currentDate = moment(new Date()).format("DD-MM-YYYY"); //to get the current date var lastDate = moment(new
Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0)).format("DD-MM-YYYY"); //month last date

This will give you current month first and last day.
If you need to change 'year' remove d.getFullYear() and set your year.
If you need to change 'month' remove d.getMonth() and set your year.
var d = new Date();
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var fistDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth(), 1).getDay())];
var LastDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth() + 1, 0).getDay())];
console.log("First Day :" + fistDayOfMonth);
console.log("Last Day:" + LastDayOfMonth);
alert("First Day :" + fistDayOfMonth);
alert("Last Day:" + LastDayOfMonth);

Try this:
function _getEndOfMonth(time_stamp) {
let time = new Date(time_stamp * 1000);
let month = time.getMonth() + 1;
let year = time.getFullYear();
let day = time.getDate();
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
day = 31;
break;
case 4:
case 6:
case 9:
case 11:
day = 30;
break;
case 2:
if (_leapyear(year))
day = 29;
else
day = 28;
break
}
let m = moment(`${year}-${month}-${day}`, 'YYYY-MM-DD')
return m.unix() + constants.DAY - 1;
}
function _leapyear(year) {
return (year % 100 === 0) ? (year % 400 === 0) : (year % 4 === 0);
}

const today = new Date();
let beginDate = new Date();
let endDate = new Date();
// fist date of montg
beginDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 1}-01 00:00:00`
);
// end date of month
// set next Month first Date
endDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 2}-01 :23:59:59`
);
// deducting 1 day
endDate.setDate(0);

Below function gives the last day of the month :
function getLstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 0).getDate()
}
console.log(getLstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 29
console.log(getLstDayOfMonFnc(new Date(2017, 2, 15))) // Output : 28
console.log(getLstDayOfMonFnc(new Date(2017, 11, 15))) // Output : 30
console.log(getLstDayOfMonFnc(new Date(2017, 12, 15))) // Output : 31
Similarly we can get first day of the month :
function getFstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 1).getDate()
}
console.log(getFstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 1

Here is an answer that conserves GMT and time of the initial date
var date = new Date();
var first_date = new Date(date); //Make a copy of the date we want the first and last days from
first_date.setUTCDate(1); //Set the day as the first of the month
var last_date = new Date(first_date); //Make a copy of the calculated first day
last_date.setUTCMonth(last_date.getUTCMonth() + 1); //Add a month
last_date.setUTCDate(0); //Set the date to 0, this goes to the last day of the previous month
console.log(first_date.toJSON().substring(0, 10), last_date.toJSON().substring(0, 10)); //Log the dates with the format yyyy-mm-dd

function getLastDay(y, m) {
return 30 + (m <= 7 ? ((m % 2) ? 1 : 0) : (!(m % 2) ? 1 : 0)) - (m == 2) - (m == 2 && y % 4 != 0 || !(y % 100 == 0 && y % 400 == 0));
}

set month you need to date and then set the day to zero ,so month begin in 1 - 31 in date function then get the last day^^
var last = new Date(new Date(new Date().setMonth(7)).setDate(0)).getDate();
console.log(last);

I know it's just a matter of semantics, but I ended up using it in this form.
var lastDay = new Date(new Date(2008, 11+1,1) - 1).getDate();
console.log(lastDay);
Since functions are resolved from the inside argument, outward, it works the same.
You can then just replace the year, and month / year with the required details, whether it be from the current date. Or a particular month / year.

If you need exact end of the month in miliseconds (for example in a timestamp):
d = new Date()
console.log(d.toString())
d.setDate(1)
d.setHours(23, 59, 59, 999)
d.setMonth(d.getMonth() + 1)
d.setDate(d.getDate() - 1)
console.log(d.toString())

The accepted answer doesn't work for me, I did it as below.
$( function() {
$( "#datepicker" ).datepicker();
$('#getLastDateOfMon').on('click', function(){
var date = $('#datepicker').val();
// Format 'mm/dd/yy' eg: 12/31/2018
var parts = date.split("/");
var lastDateOfMonth = new Date();
lastDateOfMonth.setFullYear(parts[2]);
lastDateOfMonth.setMonth(parts[0]);
lastDateOfMonth.setDate(0);
alert(lastDateOfMonth.toLocaleDateString());
});
});
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<link rel="stylesheet" href="/resources/demos/style.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<p>Date: <input type="text" id="datepicker"></p>
<button id="getLastDateOfMon">Get Last Date of Month </button>
</body>
</html>

This will give you last day of current month.
notes: on ios device include time.
#gshoanganh
var date = new Date();
console.log(new Date(date.getFullYear(), date.getMonth() + 1, 0, 23, 59, 59));

if you just need to get the last date of a month following worked out for me.
var d = new Date();
const year = d.getFullYear();
const month = d.getMonth();
const lastDay = new Date(year, month +1, 0).getDate();
console.log(lastDay);
try it out here https://www.w3resource.com/javascript-exercises/javascript-date-exercise-9.php

In my case, this code was useful
end_date = new Date(2018, 3, 1).toISOString().split('T')[0]
console.log(end_date)

JavaScript Date returns different values when the components are separated

I have a date that I want converted to a number in the format of yyyymmdd.
it comes in as
2017-08-16T05:47:42.070Z
I convert it as
let dt = new Date(dte)
which creates the date in dt of:
Wed Aug 16 2017 15:47:42 GMT+1000 (E. Australia Standard Time)
Now when I look at the parts I get the following:
dt.getFullYear() = 2017
dt.getMonth() = 7
dt.getDay() = 3
How come the day and month are off?

getMonth()
returns an integer number, between 0 and 11, representing the month in the given date according to local time. 0 corresponds to January, 1 to February, and so on.
getDay()
returns an integer number corresponding to the day of the week for the given date, according to local time: 0 for Sunday, 1 for Monday, 2 for Tuesday, and so on.
This means that result of your code is correct
dt.getFullYear() = 2017
dt.getMonth() = 7
dt.getDay() = 3
There is a function called getDate() that will return 16 for your case.
These functions are from native javascript Date Object.

You can do it like this:
function formatDate(date) {
var d = new Date(date),
month = '' + (d.getMonth() + 1),
day = '' + d.getDate(),
year = d.getFullYear();
if (month.length < 2) month = '0' + month;
if (day.length < 2) day = '0' + day;
return [year, month, day].join('-');
}
console.log(formatDate("2017-08-16T05:47:42.070Z"));

Following code return result for you:
var dte = '2017-08-16T05:47:42.070Z';
var dt = new Date(dte);
var myFrmt = dt.getFullYear().toString() + (dt.getMonth()+1).toString() + dt.getDate().toString();
alert(myFrmt);

Found out an easy way (don't know why the above doesn't work!!) using Moment
Moment(dt).format('YYYYMMDD').toString()
gives the answer: 20170816 !!

How To add number of month into the given date in javascript?

I want to add month into the select date by the user.
startdate=document.getElementById("jscal_field_coverstartdate").value;
now I want to add 11 month from the above startdate. How to do that.
date format = 2013-12-01

Without the date format it is difficult to tell, however you can try like this
add11Months = function (date) {
var splitDate = date.split("-");
var newDate = new Date(splitDate[0], splitDate[1] - 1, splitDate[2]);
newDate.setMonth(newDate.getMonth() + 11);
splitDate[2] = newDate.getDate();
splitDate[1] = newDate.getMonth() + 1;
splitDate[0] = newDate.getFullYear();
return startdate = splitDate.join("-");
}
var startdate = add11Months("2013-12-01");
alert(startdate)
JSFiddle

If your startdate is in correct date format you can try using moment.js or Date object in javascript.
In Javascript, it can be achieved as follow:
var date = new Date("2013-12-01");
console.log(date);
//output: Sun Dec 01 2013 05:30:00 GMT+0530 (India Standard Time)
var newdate = date.setDate(date.getDate()+(11*30));
console.log(new Date(newdate));
// output: Mon Oct 27 2014 05:30:00 GMT+0530 (India Standard Time)
In above lines, I have used 30 days per month as default. So you will get exact 11 month but little deviation in date. Is this what you want ? You can play around this likewise. I hope it help :)
For more about Date you can visit to MDN.

You can do it like this:
var noOfMonths = 11
var startdate = document.getElementById("jscal_field_coverstartdate").value;
startdate.setMonth(startdate.getMonth() + noOfMonths)

Try this:
baseDate.setMonth(2);
baseDate.setDate(30);
noMonths = 11;
var sum = new Date(new Date(baseDate.getTime()).setMonth(baseDate.getMonth() + noMonths);
if (sum.getDate() < baseDate.getDate()) { sum.setDate(0); }
var m = newDate.getDate();
var d = newDate.getMonth() + 1;
var yyyy = newDate.getFullYear();
return (yyyy+"-"+m+"-"+d);
Notes:
Adding months (like adding one month to January 31st) can overflow the days field and cause the month to increment (in this case you get a date in March). If you want to add months and then overflow the date then .setMonth(base_date.getMonth()+noMonths) works but that's rarely what people think of when they talk about incrementing months.
It handles cases where 29, 30 or 31 turned into 1, 2, or 3 by eliminating the overflow
Day of Month is NOT zero-indexed so .setDate(0) is last day of prior month.

How to find the next 4 days from the current day using javascript

I found the current day as Mar 27 2012 ....
var currentday = currentday.format("mmm d yyyy");
I want to find the add three days with this value.
i.e. i need the output as Mar 30 2012.
I also need to find the starting and ending date of a calendar. i.e. Feb 26 2012 - Mar 31 2012 to display the current month as displaying in calendar month view.
Can any one help me on this please....

var currentday = new Date();
var nextDay = new Date();
nextDay.setDate(currentday.getDate() + 4);

//Set number of days you want to compute to
var days=4;
//Get current date or whatever date you want to compute from
var currentDate=new Date();
var nDaysFromNow=new Date();
nDaysFromNow.setDate(currentDate.getDate()+days);

You can add days using the getDate() function like so:
var someDate = new Date();
someDate = someDate.getDate() + 3;

See code below.. Hope it helps
var days = 4;
var next = new Date((new Date).getTime() + ((1000*3600*24) *days));

Calculate last day of month

If you provide 0 as the dayValue in Date.setFullYear you get the last day of the previous month:
d = new Date(); d.setFullYear(2008, 11, 0); // Sun Nov 30 2008
There is reference to this behaviour at mozilla. Is this a reliable cross-browser feature or should I look at alternative methods?

var month = 0; // January
var d = new Date(2008, month + 1, 0);
console.log(d.toString()); // last day in January
IE 6: Thu Jan 31 00:00:00 CST 2008
IE 7: Thu Jan 31 00:00:00 CST 2008
IE 8: Beta 2: Thu Jan 31 00:00:00 CST 2008
Opera 8.54: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.27: Thu, 31 Jan 2008 00:00:00 GMT-0600
Opera 9.60: Thu Jan 31 2008 00:00:00 GMT-0600
Firefox 2.0.0.17: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Firefox 3.0.3: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Google Chrome 0.2.149.30: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Safari for Windows 3.1.2: Thu Jan 31 2008 00:00:00 GMT-0600 (Canada Central Standard Time)
Output differences are due to differences in the toString() implementation, not because the dates are different.
Of course, just because the browsers identified above use 0 as the last day of the previous month does not mean they will continue to do so, or that browsers not listed will do so, but it lends credibility to the belief that it should work the same way in every browser.

I find this to be the best solution for me. Let the Date object calculate it for you.
var today = new Date();
var lastDayOfMonth = new Date(today.getFullYear(), today.getMonth()+1, 0);
Setting day parameter to 0 means one day less than first day of the month which is last day of the previous month.

I would use an intermediate date with the first day of the next month, and return the date from the previous day:
int_d = new Date(2008, 11+1,1);
d = new Date(int_d - 1);

In computer terms, new Date() and regular expression solutions are slow! If you want a super-fast (and super-cryptic) one-liner, try this one (assuming m is in Jan=1 format). I keep trying different code changes to get the best performance.
My current fastest version:
After looking at this related question Leap year check using bitwise operators (amazing speed) and discovering what the 25 & 15 magic number represented, I have come up with this optimized hybrid of answers (note the parameters m & y must obviously be integers for this to work):
function getDaysInMonth(m, y) {
return m===2 ? y & 3 || !(y%25) && y & 15 ? 28 : 29 : 30 + (m+(m>>3)&1);
}
Given the bit-shifting this obviously assumes that your m & y parameters are both integers, as passing numbers as strings would result in weird results.
JSFiddle: http://jsfiddle.net/TrueBlueAussie/H89X3/22/
JSPerf results: http://jsperf.com/days-in-month-head-to-head/5
For some reason, (m+(m>>3)&1) is more efficient than (5546>>m&1) on almost all browsers.
The only real competition for speed is from #GitaarLab, so I have created a head-to-head JSPerf for us to test on: http://jsperf.com/days-in-month-head-to-head/5
It works based on my leap year answer here: javascript to find leap year this answer here Leap year check using bitwise operators (amazing speed) as well as the following binary logic.
A quick lesson in binary months:
If you interpret the index of the desired months (Jan = 1) in binary you will notice that months with 31 days either have bit 3 clear and bit 0 set, or bit 3 set and bit 0 clear.
Jan = 1 = 0001 : 31 days
Feb = 2 = 0010
Mar = 3 = 0011 : 31 days
Apr = 4 = 0100
May = 5 = 0101 : 31 days
Jun = 6 = 0110
Jul = 7 = 0111 : 31 days
Aug = 8 = 1000 : 31 days
Sep = 9 = 1001
Oct = 10 = 1010 : 31 days
Nov = 11 = 1011
Dec = 12 = 1100 : 31 days
That means you can shift the value 3 places with >> 3, XOR the bits with the original ^ m and see if the result is 1 or 0 in bit position 0 using & 1. Note: It turns out + is slightly faster than XOR (^) and (m >> 3) + m gives the same result in bit 0.
JSPerf results: http://jsperf.com/days-in-month-perf-test/6

My colleague stumbled upon the following which may be an easier solution
function daysInMonth(iMonth, iYear)
{
return 32 - new Date(iYear, iMonth, 32).getDate();
}
stolen from http://snippets.dzone.com/posts/show/2099

A slight modification to solution provided by lebreeze:
function daysInMonth(iMonth, iYear)
{
return new Date(iYear, iMonth, 0).getDate();
}

I recently had to do something similar, this is what I came up with:
/**
* Returns a date set to the begining of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function beginningOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1)
date.setHours(0);
date.setMinutes(0);
date.setSeconds(0);
return date;
}
/**
* Returns a date set to the end of the month
*
* #param {Date} myDate
* #returns {Date}
*/
function endOfMonth(myDate){
let date = new Date(myDate);
date.setDate(1); // Avoids edge cases on the 31st day of some months
date.setMonth(date.getMonth() +1);
date.setDate(0);
date.setHours(23);
date.setMinutes(59);
date.setSeconds(59);
return date;
}
Pass it in a date, and it will return a date set to either the beginning of the month, or the end of the month.
The begninngOfMonth function is fairly self-explanatory, but what's going in in the endOfMonth function is that I'm incrementing the month to the next month, and then using setDate(0) to roll back the day to the last day of the previous month which is a part of the setDate spec:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/setDate
https://www.w3schools.com/jsref/jsref_setdate.asp
I then set the hour/minutes/seconds to the end of the day, so that if you're using some kind of API that is expecting a date range you'll be able to capture the entirety of that last day. That part might go beyond what the original post is asking for but it could help someone else looking for a similar solution.
Edit: You can also go the extra mile and set milliseconds with setMilliseconds() if you want to be extra precise.

How NOT to do it
Beware of any answers for the last of the month that look like this:
var last = new Date(date)
last.setMonth(last.getMonth() + 1) // This is the wrong way to do it.
last.setDate(0)
This works for most dates, but fails if date is already the last day of the month, on a month that has more days than the following month.
Example:
Suppose date is 07/31/21.
Then last.setMonth(last.getMonth() + 1) increments the month, but keeps the day set at 31.
You get a Date object for 08/31/21,
which is actually 09/01/21.
So then last.setDate(0) results in 08/31/21 when what we really wanted was 07/31/21.

try this one.
lastDateofTheMonth = new Date(year, month, 0)
example:
new Date(2012, 8, 0)
output:
Date {Fri Aug 31 2012 00:00:00 GMT+0900 (Tokyo Standard Time)}

This works for me.
Will provide last day of given year and month:
var d = new Date(2012,02,0);
var n = d.getDate();
alert(n);

This one works nicely:
Date.prototype.setToLastDateInMonth = function () {
this.setDate(1);
this.setMonth(this.getMonth() + 1);
this.setDate(this.getDate() - 1);
return this;
}

You can get the First and Last Date in the current month by following the code:
var dateNow = new Date();
var firstDate = new Date(dateNow.getFullYear(), dateNow.getMonth(), 1);
var lastDate = new Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0);
or if you want to format the date in your custom format then you can use moment js
var dateNow= new Date();
var firstDate=moment(new Date(dateNow.getFullYear(),dateNow.getMonth(), 1)).format("DD-MM-YYYY");
var currentDate = moment(new Date()).format("DD-MM-YYYY"); //to get the current date var lastDate = moment(new
Date(dateNow.getFullYear(), dateNow.getMonth() + 1, 0)).format("DD-MM-YYYY"); //month last date

This will give you current month first and last day.
If you need to change 'year' remove d.getFullYear() and set your year.
If you need to change 'month' remove d.getMonth() and set your year.
var d = new Date();
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var fistDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth(), 1).getDay())];
var LastDayOfMonth = days[(new Date(d.getFullYear(), d.getMonth() + 1, 0).getDay())];
console.log("First Day :" + fistDayOfMonth);
console.log("Last Day:" + LastDayOfMonth);
alert("First Day :" + fistDayOfMonth);
alert("Last Day:" + LastDayOfMonth);

Try this:
function _getEndOfMonth(time_stamp) {
let time = new Date(time_stamp * 1000);
let month = time.getMonth() + 1;
let year = time.getFullYear();
let day = time.getDate();
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
day = 31;
break;
case 4:
case 6:
case 9:
case 11:
day = 30;
break;
case 2:
if (_leapyear(year))
day = 29;
else
day = 28;
break
}
let m = moment(`${year}-${month}-${day}`, 'YYYY-MM-DD')
return m.unix() + constants.DAY - 1;
}
function _leapyear(year) {
return (year % 100 === 0) ? (year % 400 === 0) : (year % 4 === 0);
}

const today = new Date();
let beginDate = new Date();
let endDate = new Date();
// fist date of montg
beginDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 1}-01 00:00:00`
);
// end date of month
// set next Month first Date
endDate = new Date(
`${today.getFullYear()}-${today.getMonth() + 2}-01 :23:59:59`
);
// deducting 1 day
endDate.setDate(0);

Below function gives the last day of the month :
function getLstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 0).getDate()
}
console.log(getLstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 29
console.log(getLstDayOfMonFnc(new Date(2017, 2, 15))) // Output : 28
console.log(getLstDayOfMonFnc(new Date(2017, 11, 15))) // Output : 30
console.log(getLstDayOfMonFnc(new Date(2017, 12, 15))) // Output : 31
Similarly we can get first day of the month :
function getFstDayOfMonFnc(date) {
return new Date(date.getFullYear(), date.getMonth(), 1).getDate()
}
console.log(getFstDayOfMonFnc(new Date(2016, 2, 15))) // Output : 1

Here is an answer that conserves GMT and time of the initial date
var date = new Date();
var first_date = new Date(date); //Make a copy of the date we want the first and last days from
first_date.setUTCDate(1); //Set the day as the first of the month
var last_date = new Date(first_date); //Make a copy of the calculated first day
last_date.setUTCMonth(last_date.getUTCMonth() + 1); //Add a month
last_date.setUTCDate(0); //Set the date to 0, this goes to the last day of the previous month
console.log(first_date.toJSON().substring(0, 10), last_date.toJSON().substring(0, 10)); //Log the dates with the format yyyy-mm-dd

function getLastDay(y, m) {
return 30 + (m <= 7 ? ((m % 2) ? 1 : 0) : (!(m % 2) ? 1 : 0)) - (m == 2) - (m == 2 && y % 4 != 0 || !(y % 100 == 0 && y % 400 == 0));
}

set month you need to date and then set the day to zero ,so month begin in 1 - 31 in date function then get the last day^^
var last = new Date(new Date(new Date().setMonth(7)).setDate(0)).getDate();
console.log(last);

I know it's just a matter of semantics, but I ended up using it in this form.
var lastDay = new Date(new Date(2008, 11+1,1) - 1).getDate();
console.log(lastDay);
Since functions are resolved from the inside argument, outward, it works the same.
You can then just replace the year, and month / year with the required details, whether it be from the current date. Or a particular month / year.

If you need exact end of the month in miliseconds (for example in a timestamp):
d = new Date()
console.log(d.toString())
d.setDate(1)
d.setHours(23, 59, 59, 999)
d.setMonth(d.getMonth() + 1)
d.setDate(d.getDate() - 1)
console.log(d.toString())

The accepted answer doesn't work for me, I did it as below.
$( function() {
$( "#datepicker" ).datepicker();
$('#getLastDateOfMon').on('click', function(){
var date = $('#datepicker').val();
// Format 'mm/dd/yy' eg: 12/31/2018
var parts = date.split("/");
var lastDateOfMonth = new Date();
lastDateOfMonth.setFullYear(parts[2]);
lastDateOfMonth.setMonth(parts[0]);
lastDateOfMonth.setDate(0);
alert(lastDateOfMonth.toLocaleDateString());
});
});
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<link rel="stylesheet" href="/resources/demos/style.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<p>Date: <input type="text" id="datepicker"></p>
<button id="getLastDateOfMon">Get Last Date of Month </button>
</body>
</html>

This will give you last day of current month.
notes: on ios device include time.
#gshoanganh
var date = new Date();
console.log(new Date(date.getFullYear(), date.getMonth() + 1, 0, 23, 59, 59));

if you just need to get the last date of a month following worked out for me.
var d = new Date();
const year = d.getFullYear();
const month = d.getMonth();
const lastDay = new Date(year, month +1, 0).getDate();
console.log(lastDay);
try it out here https://www.w3resource.com/javascript-exercises/javascript-date-exercise-9.php

In my case, this code was useful
end_date = new Date(2018, 3, 1).toISOString().split('T')[0]
console.log(end_date)

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