Develop Reference

How to generate date from current days to last days in Javascript?

I want to generate date as my below PHP code in Javascript But I don't know how to do.
$begin2 = new DateTime(date("Y-m-d", strtotime("-5 day")));
$interval2 = new DateInterval('P1D');
$end2 = new DateTime(date("Y-m-d", strtotime("+1 day")));
$daterange2 = new DatePeriod($begin2, $interval2, $end2);
foreach (array_reverse(iterator_to_array($daterange2)) as $val) {
echo $val->format("Ymd");
}
Output:
2015-12-04
2015-12-03
2015-12-02
2015-12-01
2015-11-30
2015-11-29
2015-11-28
2015-11-27
2015-11-26
2015-11-25

Edit
Wow, completely missed the point of the question!
Seems you want dates from today going backwards for a set number of days in ISO 8601 format. The Date constructor will create a date, and Date.prototype.toISOString will return an ISO 8601 date. It just needs the time part trimmed.
So a function to returns date strings for all the dates from today going back n days is:
function getDateRange(n) {
var d = new Date(),
dates = [];
while (n--) {
dates.push(d.toISOString().split('T')[0]);
d.setDate(d.getDate() - 1);
}
return dates;
}
// Example
document.write(getDateRange(10).join('<br>'));
Original answer
The only reliable way to parse date strings in javascript is to do it manually. A library can help, but a bespoke function isn't much work:
function parseYMD(s) {
var b = s.split(/\D/);
return new Date(b[0], b[1]-1, b[2]);
}
document.write(parseYMD('2015-12-04'))
This assumes the string is a valid date and will parse the string to a local Date, consistent with ECMAScript 2015 (and ISO 8601). If you need to also validate the string, a couple of extra lines are required.

Native "Date" will be enough for some date operations.
var myDate = new Date();
var dateLate = new Date();
var dateEarly = new Date();
dateLate.setDate(dateLate.getDate() + 10);
dateEarly.setDate(dateEarly.getDate() - 10);
myDate.setDate(dateLate.getDate());
while (myDate.getDate() != dateEarly.getDate()) {
myDate.setDate(myDate.getDate() - 1);
document.write(myDate.toLocaleDateString() + '<br>');
}
You can format the date in a different way.

Here's the code doing an iteration in reverse order for your given dates
var now = new Date();
var begin2 = new Date();
var end2 = new Date();
var year, month, day, datestr;
begin2.setDate(now.getDate() - 5);
end2.setDate(now.getDate() + 1);
var current = begin2;
var resulting_dates = [];
while (current <= end2) {
datestr = current.getFullYear() + '-' + ('0' + (current.getMonth() + 1)).slice(-2) + '-' + ('0' + current.getDate()).slice(-2);
resulting_dates.push(datestr);
current.setDate(current.getDate() + 1);
}
console.log(resulting_dates);

How to get the date trimmed of exactly in the format of (dd/mm/yyyy) in the following implementation of my code using JavaScript

How to get the date trimmed of exactly in the format of (dd/mm/yyyy) in the following implementation of my code using JavaScript
<script type="text/javascript" language="javascript">
function disptextbox() {
var d = new Date();
var x = document.getElementById("ddlweeklist").value;
switch (x)
{
case "1":
document.getElementById("txtstart").value = d.toDateString();
document.getElementById("Txtend").value = d.toDateString();
break;
case "2":
var firstday = new Date(d.setDate(d.getDate() - d.getDay()));
var lastday = new Date(d.setDate(d.getDate() - d.getDay() + 6));
document.getElementById("txtstart").value= firstday.toDateString();
document.getElementById("Txtend").value = lastday.toDateString();
break;
case "3":
var date = new Date();
var firstDay = new Date(date.getFullYear(), date.getMonth(), 1);
var lastDay = new Date(date.getFullYear(), date.getMonth() + 1, 0);
document.getElementById("txtstart").value = firstDay.toDateString();
document.getElementById("Txtend").value = lastDay.toDateString();
break;
case "4":
var firstd = new Date(d.getFullYear(), 0, 1);
var lastd = new Date(d.getFullYear(), 11, 31);
document.getElementById("txtstart").value = firstd.toDateString();
document.getElementById("Txtend").value = lastd.toDateString();
break;
}
}
</script>
in this code of implementation I want the date format to be in dd/mm/yyyy format ...I will be glad if any one help me over this this function call occurs on the drop down change especially...I am ok with functionality of the code but not comfortable in handling with DATE FUNCTIONS...
so please suggest me where I can get good examples for implementing date functions...in javascript

You can do this if you want dd/mm/yyyy format date:
new Date().toISOString().substr(0,10).replace(/(\d{4})-(\d{2})-(\d{2})/g,"$3/$2/$1");

I've written a couple of prototypes for dates than you may find useful:
Date.prototype.dateStr=function(split){
split=split===undefined?"-":split;
var output=parseInt(parseInt(this.getMonth())+1).toString().toLength(2);
output+=split;
output+=this.getDate().toString().toLength(2);
output+=split;
output+=this.getFullYear().toString().toLength(4);
return output;
}
Date.prototype.FOM=function(){
return new Date(this.getFullYear(),this.getMonth(),1);
}
String.prototype.toLength=function(len,fill){
fill=fill===undefined?"0":fill;
var outStr=this.toString();
while (outStr.length<parseInt(len)){
outStr=fill+outStr;
}
return outStr;
}
Technically, the 3rd one is a string prototype, but whatever. new Date().FOM() will give you a javascript date object for the first day of whatever month you pass it. new Date().dateStr("/") will give you a string - mm/dd/yyyy format - with separators as whatever you pass it, default "-".
That last one will take a string and make it a certain length by prepending the 'fill' - default '0'.

You could try with this function:
function toDateString(mydate) {
var day = mydate.getDate();
var month = mydate.getMonth();
day = day < 10 ? '0'+day : day;
month = month < 10 ? '0'+month : month;
return day + '/' + month + '/' + mydate.getYear();
}
You could then use it this way:
alert(toDateString(firstday)); // I'm using alert just for demonstration purposes
Here is a DEMO you could fiddle with.
EDITED: Learning from #Helpful's answer below, my above function could be used as a prototype to better fit the way you wrote up your code like this:
Date.prototype.toDateString=function() {
var day = this.getDate();
var month = this.getMonth();
day = day < 10 ? '0'+day : day;
month = month < 10 ? '0'+month : month;
return day + '/' + month + '/' + this.getYear();
}
so you could call it this way:
alert(thedate.toDateString()); // This is how you used it, if I understood it well.
Here is a DEMO of that.

Pass any data format
function convertDate(inputFormat) {
function pad(s) { return (s < 10) ? '0' + s : s; }
var d = new Date(inputFormat);
return [pad(d.getDate()), pad(d.getMonth()+1), d.getFullYear()].join('/');
}
hope this will help you sure.....

compare string with today's date in JavaScript

I've got a string from an input field which I use for date with a format like this 25-02-2013. Now I want to compare the string with today's date. I want to know if the string is older or newer then today's date.
Any suggestions?

<script type="text/javascript">
var q = new Date();
var m = q.getMonth()+1;
var d = q.getDay();
var y = q.getFullYear();
var date = new Date(y,m,d);
mydate=new Date('2011-04-11');
console.log(date);
console.log(mydate)
if(date>mydate)
{
alert("greater");
}
else
{
alert("smaller")
}
</script>

Exact date comparsion and resolved bug from accepted answer
var q = new Date();
var m = q.getMonth();
var d = q.getDay();
var y = q.getFullYear();
var date = new Date(y,m,d);
mydate=new Date('2011-04-11');
console.log(date);
console.log(mydate)
if(date>mydate)
{
alert("greater");
}
else
{
alert("smaller")
}

You can use a simple comparison operator to see if a date is greater than another:
var today = new Date();
var jun3 = new Date("2016-06-03 0:00:00");
if(today > jun3){
// True if today is on or after June 3rd 2016
}else{
// Today is before June 3rd
}
The reason why I added 0:00:00 to the second variable is because without it, it'll compare to UTC (Greenwich) time, which may give you undesired results. If you set the time to 0, then it'll compare to the user's local midnight.

Using Javascript Date object will be easier for you. But as the Date object does not supports your format i think you have to parse your input string(eg: 25-02-2013) with '-' to get date month and year and then use Date object for comparison.
var x ='23-5-2010';
var a = x.split('-');
var date = new Date (a[2], a[1] - 1,a[0]);//using a[1]-1 since Date object has month from 0-11
var Today = new Date();
if (date > Today)
alert("great");
else
alert("less");

If your date input is in the format "25-02-2013", you can split the string into DD, MM and YYYY using the split() method:
var date_string="25-02-2013";
var day = parseInt(date_string.split("-")[0]);
var month= parseInt(date_string.split("-")[1]);
var year = parseInt(date_string.split("-")[2]);
The parseInt() function is used to make the string into an integer. The 3 variables can then be compared against properties of the Date() object.

The most significant points which needs to be remembered while doing date comparison
Both the dates should be in same format to get accurate result.
If you are using date time format and only wants to do date comparison then make sure you convert it in related format.
Here is the code which I used.
var dateNotifStr = oRecord.getData("dateNotif");
var today = new Date();
var todayDateFormatted = new Date(today.getFullYear(),today.getMonth(),today.getDate());
var dateNotif=new Date(dateNotifStr);
var dateNotifFormatted = new Date(dateNotif.getFullYear(),dateNotif.getMonth(),dateNotif.getDate());
Well, this can be optimized further but this should give you clear idea on what is required to make dates in uniform format.

Here's my solution, getDay() doesn't work like some people said because it grabs the day of the week and not the day of the month. So instead you should use getDate like I used below
var date = new Date();
var m = date.getMonth();
var d = date.getDate();
var y = date.getFullYear();
var todaysDate = formateDate(new Date(y,m,d));
console.log("Todays date is: " + todaysDate)
const formateDate = (assignmentDate) => {
const date = new Date(assignmentDate)
const formattedDate = date.toLocaleDateString("en-GB", {
day: "numeric",
month: "long",
year: "numeric"
})
return formattedDate
}
The function below is just to format the date into a legible format I could display to my users

<script type="text/javascript">
// If you set the timezone then your condition will work properly,
// otherwise there is a possibility of error,
// because timezone is a important part of date function
var todayDate = new Date().toLocaleString([], { timeZone: "Asia/Dhaka" }); //Today Date
var targetDate = new Date('2022-11-24').toLocaleString([], { timeZone: "Asia/Dhaka" });
console.log('todayDate ==', todayDate); // todayDate == 10/31/2022, 12:15:08 PM
console.log('targetDate ==', targetDate); // targetDate == 11/24/2022, 6:00:00 AM
if(targetDate >= todayDate)
{
console.log("Today's date is small");
}
else
{
console.log("Today's date is big")
}
</script>

Regular expression for date format- dd-mm-yyyy in Javascript

I need a regular expression for date format: dd-mm-yyyy in Javascript.

function parseDate(str) {
var m = str.match(/^(\d{1,2})-(\d{1,2})-(\d{4})$/);
return (m) ? new Date(m[3], m[2]-1, m[1]) : null;
}

Notice
Your regexp does not work for years that "are multiples of 4 and 100, but not of 400". Years that pass that test are not leap years. For example: 1900, 2100, 2200, 2300, 2500, etc. In other words, it puts all years with the format \d\d00 in the same class of leap years, which is incorrect. – MuchToLearn
So it works properly only for [1901 - 2099] (Whew) 😊
dd-MM-yyyy
Checks if leap year.
Years from 1900 to 9999 are valid. Only dd-MM-yyyy
var stringToValidate = "29-02-2012";
var rgexp = /(^(((0[1-9]|1[0-9]|2[0-8])[-](0[1-9]|1[012]))|((29|30|31)[-](0[13578]|1[02]))|((29|30)[-](0[4,6,9]|11)))[-](19|[2-9][0-9])\d\d$)|(^29[-]02[-](19|[2-9][0-9])(00|04|08|12|16|20|24|28|32|36|40|44|48|52|56|60|64|68|72|76|80|84|88|92|96)$)/;
var isValidDate = rgexp.test(stringToValidate);

Here is Regex for multiple date formats working for me :
//dd.MM.yyyy
var date_regex = /^(0[1-9]|1\d|2\d|3[01])\.(0[1-9]|1[0-2])\.(19|20)\d{2}$/;
alert(date_regex.test("02.02.1991"));
// //dd/mm/yyyy
// var date_regex = /^(0[1-9]|1\d|2\d|3[01])\/(0[1-9]|1[0-2])\/(19|20)\d{2}$/;
// alert(date_regex.test("02/12/1991"));
// //dd-mm-yyyy
// var date_regex = /^(0[1-9]|1\d|2\d|3[01])\-(0[1-9]|1[0-2])\-(19|20)\d{2}$/;
// alert(date_regex.test("02-12-1991"));
// //mm/dd/yyyy
// var date_regex = /^(0[1-9]|1[0-2])\/(0[1-9]|1\d|2\d|3[01])\/(19|20)\d{2}$/;
// alert(date_regex.test("12/02/1991"));
// //yyyy.MM.dd
// var date_regex = /^((19|20)\d{2})\.(0[1-9]|1[0-2])\.(0[1-9]|1\d|2\d|3[01])$/;
// alert(date_regex.test("1991.12.02"));
// //yyyy/MM/dd
// var date_regex = /^((19|20)\d{2})\/(0[1-9]|1[0-2])\/(0[1-9]|1\d|2\d|3[01])$/;
// alert(date_regex.test("1991/12/02"));
// //yyyy-MM-dd
// var date_regex = /^((19|20)\d{2})\-(0[1-9]|1[0-2])\-(0[1-9]|1\d|2\d|3[01])$/;
// alert(date_regex.test("1991-12-02"));

Try this:
'01-01-2012'.match( /\d{2}-\d{2}-\d{4}/ )
Note that that this way the date 33-12-2022 would be considered valid as well!

'01-01-2012'.match( /(?!3[2-9]|00|02-3[01]|04-31|06-31|09-31|11-31)[0-3][0-9]-(?!1[3-9]|00)[01][0-9]-(?!10|28|29)[12][089][0-9][0-9]/ )
This looks for only valid dates from 1800 to 2099. No leap year support (as in it assumes every year is a possible leap year).

Well, I made this:
'31-12-1987'.match(/(3[01]|[2][0-9]|0\d)-(1[0-2]|0\[1-9])-\d{4}/)
Validates the day from 01 to 31, month from 01 to 12 and year of four digits. It only fails the february 30, and the months without 31 days. Which you can clean using the new Date('mm/dd/yyyy').

This regex is for MM/DD/YYYY and M/D/YYYY
var date_regex = /^(0?[1-9]|1[012])[\/](0?[1-9]|[12][0-9]|3[01])[\/]\d{4}$/;

Working a few of the above together (primarily #gdZeus's) now you can do MM/dd/yyyy | MM-dd-yyyy | MM.dd.yyyy
/(^(((0[1-9]|1[012])[-/.](0[1-9]|1[0-9]|2[0-8]))|((0[13578]|1[02])[-/.](29|30|31))|((0[4,6,9]|11)[-/.](29|30)))[-/.](19|[2-9][0-9])\d\d$)|(^02[-/.]29[-/.](19|[2-9][0-9])(00|04|08|12|16|20|24|28|32|36|40|44|48|52|56|60|64|68|72|76|80|84|88|92|96)$)/
Additionally if you are using this inline in a js file you can use the following which returns a regexp literal. This will allow you to validate that a date is in the past! This is handy for birthdays. You can reverse it to check that a date is in the future as well (ex. checking credit card exp). This will work almost anywhere in javascript but not if you really need a regexp literal. For example if you are serializing it to a some other format without the ability to run js.
new RegExp('(^(((0[1-9]|1[012])[-/.](0[1-9]|1[0-9]|2[0-8]))|((0[13578]|1[02])[-/.](29|30|31))|((0[4,6,9]|11)[-/.](29|30)))[-/.]('+range(1920, new Date().getFullYear()).join('|')+')$)|(^02[-/.]29[-/.]('+range(1920, new Date().getFullYear()).filter(function(year){if (year % 4 == 0) { return true }}).join('|')+')$)/', 'g')
returns:
/(^(((0[1-9]|1[012])[-\/.](0[1-9]|1[0-9]|2[0-8]))|((0[13578]|1[02])[-\/.](29|30|31))|((0[4,6,9]|11)[-\/.](29|30)))[-\/.](1920|1921|1922|1923|1924|1925|1926|1927|1928|1929|1930|1931|1932|1933|1934|1935|1936|1937|1938|1939|1940|1941|1942|1943|1944|1945|1946|1947|1948|1949|1950|1951|1952|1953|1954|1955|1956|1957|1958|1959|1960|1961|1962|1963|1964|1965|1966|1967|1968|1969|1970|1971|1972|1973|1974|1975|1976|1977|1978|1979|1980|1981|1982|1983|1984|1985|1986|1987|1988|1989|1990|1991|1992|1993|1994|1995|1996|1997|1998|1999|2000|2001|2002|2003|2004|2005|2006|2007|2008|2009|2010|2011|2012|2013|2014|2015)$)|(^02[-\/.]29[-\/.](1920|1924|1928|1932|1936|1940|1944|1948|1952|1956|1960|1964|1968|1972|1976|1980|1984|1988|1992|1996|2000|2004|2008|2012)$)\//g
NOTE: this utilizes underscore's range function to generate the dates. You can write your own though like this very inelegant version :)
function range(start, end) {
var foo = [];
for (var i = start; i <= end; i++) {
foo.push(i);
}
return foo;
}

$('#DOB').blur(function () {
var s = $('#DOB').val(); alert('Entered date is:' + s);
var parms = s.split(/[\.\-\/]/);
var yyyy = parseInt(parms[2], 10);
var d = new Date();
var n = d.getFullYear(); //alert('current year is :' + n);
if (yyyy > n || yyyy < 1900) {
alert('Improper date format, Please enter dd/mm/yyyy format. (invalid year)');
}
var mm = parseInt(parms[1], 10);
if (mm > 12 || mm < 0)
{
alert('Improper date format, Please enter dd/mm/yyyy format. (invalid month');
}
var dd = parseInt(parms[0], 10);
if (dd > 31 || dd < 0)
{
alert('Improper date format, Please enter dd/mm/yyyy format. (invalid day');
}
//var date = new Date(dd, mm - 1, yyyy, 12, 0, 0, 0);
//var ndate = (date.getMonth() + 1) && ddmm === date.getDate() && yyyy === date.getFullYear();
// alert('new date is:' + ndate);
});

This works for me
new RegExp('^(0[1-9]|[1-9]|[12][0-9]|3[01])-(0[1-9]|[1-9]|1[012])-(19|20)\\d\\d$')

/^(\d{1,2})(\/)(\d{1,2})\2(\d{4})\$/

Get String in YYYYMMDD format from JS date object?

I'm trying to use JS to turn a date object into a string in YYYYMMDD format. Is there an easier way than concatenating Date.getYear(), Date.getMonth(), and Date.getDay()?

Altered piece of code I often use:
Date.prototype.yyyymmdd = function() {
var mm = this.getMonth() + 1; // getMonth() is zero-based
var dd = this.getDate();
return [this.getFullYear(),
(mm>9 ? '' : '0') + mm,
(dd>9 ? '' : '0') + dd
].join('');
};
var date = new Date();
date.yyyymmdd();

I didn't like adding to the prototype. An alternative would be:
var rightNow = new Date();
var res = rightNow.toISOString().slice(0,10).replace(/-/g,"");
<!-- Next line is for code snippet output only -->
document.body.innerHTML += res;

You can use the toISOString function :
var today = new Date();
today.toISOString().substring(0, 10);
It will give you a "yyyy-mm-dd" format.

Moment.js could be your friend
var date = new Date();
var formattedDate = moment(date).format('YYYYMMDD');

new Date('Jun 5 2016').
toLocaleString('en-us', {year: 'numeric', month: '2-digit', day: '2-digit'}).
replace(/(\d+)\/(\d+)\/(\d+)/, '$3-$1-$2');
// => '2016-06-05'

If you don't need a pure JS solution, you can use jQuery UI to do the job like this :
$.datepicker.formatDate('yymmdd', new Date());
I usually don't like to import too much libraries. But jQuery UI is so useful, you will probably use it somewhere else in your project.
Visit http://api.jqueryui.com/datepicker/ for more examples

This is a single line of code that you can use to create a YYYY-MM-DD string of today's date.
var d = new Date().toISOString().slice(0,10);

I don't like modifying native objects, and I think multiplication is clearer than the string padding the accepted solution.
function yyyymmdd(dateIn) {
var yyyy = dateIn.getFullYear();
var mm = dateIn.getMonth() + 1; // getMonth() is zero-based
var dd = dateIn.getDate();
return String(10000 * yyyy + 100 * mm + dd); // Leading zeros for mm and dd
}
var today = new Date();
console.log(yyyymmdd(today));
Fiddle: http://jsfiddle.net/gbdarren/Ew7Y4/

In addition to o-o's answer I'd like to recommend separating logic operations from the return and put them as ternaries in the variables instead.
Also, use concat() to ensure safe concatenation of variables
Date.prototype.yyyymmdd = function() {
var yyyy = this.getFullYear();
var mm = this.getMonth() < 9 ? "0" + (this.getMonth() + 1) : (this.getMonth() + 1); // getMonth() is zero-based
var dd = this.getDate() < 10 ? "0" + this.getDate() : this.getDate();
return "".concat(yyyy).concat(mm).concat(dd);
};
Date.prototype.yyyymmddhhmm = function() {
var yyyymmdd = this.yyyymmdd();
var hh = this.getHours() < 10 ? "0" + this.getHours() : this.getHours();
var min = this.getMinutes() < 10 ? "0" + this.getMinutes() : this.getMinutes();
return "".concat(yyyymmdd).concat(hh).concat(min);
};
Date.prototype.yyyymmddhhmmss = function() {
var yyyymmddhhmm = this.yyyymmddhhmm();
var ss = this.getSeconds() < 10 ? "0" + this.getSeconds() : this.getSeconds();
return "".concat(yyyymmddhhmm).concat(ss);
};
var d = new Date();
document.getElementById("a").innerHTML = d.yyyymmdd();
document.getElementById("b").innerHTML = d.yyyymmddhhmm();
document.getElementById("c").innerHTML = d.yyyymmddhhmmss();
<div>
yyyymmdd: <span id="a"></span>
</div>
<div>
yyyymmddhhmm: <span id="b"></span>
</div>
<div>
yyyymmddhhmmss: <span id="c"></span>
</div>

Local time:
var date = new Date();
date = date.toJSON().slice(0, 10);
UTC time:
var date = new Date().toISOString();
date = date.substring(0, 10);
date will print 2020-06-15 today as i write this.
toISOString() method returns the date with the ISO standard which is YYYY-MM-DDTHH:mm:ss.sssZ
The code takes the first 10 characters that we need for a YYYY-MM-DD format.
If you want format without '-' use:
var date = new Date();
date = date.toJSON().slice(0, 10).split`-`.join``;
In .join`` you can add space, dots or whatever you'd like.

Plain JS (ES5) solution without any possible date jump issues caused by Date.toISOString() printing in UTC:
var now = new Date();
var todayUTC = new Date(Date.UTC(now.getFullYear(), now.getMonth(), now.getDate()));
return todayUTC.toISOString().slice(0, 10).replace(/-/g, '');
This in response to #weberste's comment on #Pierre Guilbert's answer.

// UTC/GMT 0
document.write('UTC/GMT 0: ' + (new Date()).toISOString().slice(0, 19).replace(/[^0-9]/g, "")); // 20150812013509
// Client local time
document.write('<br/>Local time: ' + (new Date(Date.now()-(new Date()).getTimezoneOffset() * 60000)).toISOString().slice(0, 19).replace(/[^0-9]/g, "")); // 20150812113509

Another way is to use toLocaleDateString with a locale that has a big-endian date format standard, such as Sweden, Lithuania, Hungary, South Korea, ...:
date.toLocaleDateString('se')
To remove the delimiters (-) is just a matter of replacing the non-digits:
console.log( new Date().toLocaleDateString('se').replace(/\D/g, '') );
This does not have the potential error you can get with UTC date formats: the UTC date may be one day off compared to the date in the local time zone.

var someDate = new Date();
var dateFormated = someDate.toISOString().substr(0,10);
console.log(dateFormated);

dateformat is a very used package.
How to use:
Download and install dateformat from NPM. Require it in your module:
const dateFormat = require('dateformat');
and then just format your stuff:
const myYYYYmmddDate = dateformat(new Date(), 'yyyy-mm-dd');

Shortest
.toJSON().slice(0,10).split`-`.join``;
let d = new Date();
let s = d.toJSON().slice(0,10).split`-`.join``;
console.log(s);

Working from #o-o's answer this will give you back the string of the date according to a format string. You can easily add a 2 digit year regex for the year & milliseconds and the such if you need them.
Date.prototype.getFromFormat = function(format) {
var yyyy = this.getFullYear().toString();
format = format.replace(/yyyy/g, yyyy)
var mm = (this.getMonth()+1).toString();
format = format.replace(/mm/g, (mm[1]?mm:"0"+mm[0]));
var dd = this.getDate().toString();
format = format.replace(/dd/g, (dd[1]?dd:"0"+dd[0]));
var hh = this.getHours().toString();
format = format.replace(/hh/g, (hh[1]?hh:"0"+hh[0]));
var ii = this.getMinutes().toString();
format = format.replace(/ii/g, (ii[1]?ii:"0"+ii[0]));
var ss = this.getSeconds().toString();
format = format.replace(/ss/g, (ss[1]?ss:"0"+ss[0]));
return format;
};
d = new Date();
var date = d.getFromFormat('yyyy-mm-dd hh:ii:ss');
alert(date);
I don't know how efficient that is however, especially perf wise because it uses a lot of regex. It could probably use some work I do not master pure js.
NB: I've kept the predefined class definition but you might wanna put that in a function or a custom class as per best practices.

A little variation for the accepted answer:
function getDate_yyyymmdd() {
const date = new Date();
const yyyy = date.getFullYear();
const mm = String(date.getMonth() + 1).padStart(2,'0');
const dd = String(date.getDate()).padStart(2,'0');
return `${yyyy}${mm}${dd}`
}
console.log(getDate_yyyymmdd())

This guy here => http://blog.stevenlevithan.com/archives/date-time-format wrote a format() function for the Javascript's Date object, so it can be used with familiar literal formats.
If you need full featured Date formatting in your app's Javascript, use it. Otherwise if what you want to do is a one off, then concatenating getYear(), getMonth(), getDay() is probably easiest.

Little bit simplified version for the most popular answer in this thread https://stackoverflow.com/a/3067896/5437379 :
function toYYYYMMDD(d) {
var yyyy = d.getFullYear().toString();
var mm = (d.getMonth() + 101).toString().slice(-2);
var dd = (d.getDate() + 100).toString().slice(-2);
return yyyy + mm + dd;
}

You can simply use This one line code to get date in year
var date = new Date().getFullYear() + "-" + (parseInt(new Date().getMonth()) + 1) + "-" + new Date().getDate();

How about Day.js?
It's only 2KB, and you can also dayjs().format('YYYY-MM-DD').
https://github.com/iamkun/dayjs

Use padStart:
Date.prototype.yyyymmdd = function() {
return [
this.getFullYear(),
(this.getMonth()+1).toString().padStart(2, '0'), // getMonth() is zero-based
this.getDate().toString().padStart(2, '0')
].join('-');
};

This code is fix to Pierre Guilbert's answer:
(it works even after 10000 years)
YYYYMMDD=new Date().toISOString().slice(0,new Date().toISOString().indexOf("T")).replace(/-/g,"")

Answering another for Simplicity & readability.
Also, editing existing predefined class members with new methods is not encouraged:
function getDateInYYYYMMDD() {
let currentDate = new Date();
// year
let yyyy = '' + currentDate.getFullYear();
// month
let mm = ('0' + (currentDate.getMonth() + 1)); // prepend 0 // +1 is because Jan is 0
mm = mm.substr(mm.length - 2); // take last 2 chars
// day
let dd = ('0' + currentDate.getDate()); // prepend 0
dd = dd.substr(dd.length - 2); // take last 2 chars
return yyyy + "" + mm + "" + dd;
}
var currentDateYYYYMMDD = getDateInYYYYMMDD();
console.log('currentDateYYYYMMDD: ' + currentDateYYYYMMDD);

[day,,month,,year]= Intl.DateTimeFormat(undefined, { year: 'numeric', month: '2-digit', day: '2-digit' }).formatToParts(new Date()),year.value+month.value+day.value
or
new Date().toJSON().slice(0,10).replace(/\/|-/g,'')

From ES6 onwards you can use template strings to make it a little shorter:
var now = new Date();
var todayString = `${now.getFullYear()}-${now.getMonth()}-${now.getDate()}`;
This solution does not zero pad. Look to the other good answers to see how to do that.

I usually use the code below when I need to do this.
var date = new Date($.now());
var dateString = (date.getFullYear() + '-'
+ ('0' + (date.getMonth() + 1)).slice(-2)
+ '-' + ('0' + (date.getDate())).slice(-2));
console.log(dateString); //Will print "2015-09-18" when this comment was written
To explain, .slice(-2) gives us the last two characters of the string.
So no matter what, we can add "0" to the day or month, and just ask for the last two since those are always the two we want.
So if the MyDate.getMonth() returns 9, it will be:
("0" + "9") // Giving us "09"
so adding .slice(-2) on that gives us the last two characters which is:
("0" + "9").slice(-2)
"09"
But if date.getMonth() returns 10, it will be:
("0" + "10") // Giving us "010"
so adding .slice(-2) gives us the last two characters, or:
("0" + "10").slice(-2)
"10"

It seems that mootools provides Date().format(): https://mootools.net/more/docs/1.6.0/Types/Date
I'm not sure if it worth including just for this particular task though.

If you don't mind including an additional (but small) library, Sugar.js provides lots of nice functionality for working with dates in JavaScript.
To format a date, use the format function:
new Date().format("{yyyy}{MM}{dd}")