I didn't like adding to the prototype. An alternative would be:

const rightNow = new Date();
const 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 in 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/

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.

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>

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.

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.

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');

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())

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;
}

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.

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.

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();

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('-');
};

[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,'')

const date = new Date()

console.log(date.toISOString().split('T')[0]) // 2022-12-27

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);

How about Day.js?

It's only 2KB, and you can also dayjs().format('YYYY-MM-DD').

https://github.com/iamkun/dayjs

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}")

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.