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Why am I getting this error for JavaScript Date object?

I wrote the following code in JS
var d = new Date(2019, 9, 14);
var currentTime = d.getTime();
var daysToAdd = 3;
var secondsInDay = 86400;
var d = new Date(currentTime + daysToAdd*secondsInDay);
var year = d.getFullYear();
var month = ("0" + (d.getMonth())).slice(-2);
var day = ("0" + d.getDate()).slice(-2);
console.log('result in Y-M-D is: ' + year + '-' + month + '-' + day);
This outputs to result in Y-M-D is: 2019-09-14
What am I doing wrong here? How to I change this to output result in Y-M-D is: 2019-09-17 , which I originally intended to do

This happens because on this code
new Date(currentTime + daysToAdd*secondsInDay);
secondsInDay is a representation in seconds, and currentTime is represented in ms. If you multiply your secondsInDay by 1000 (to get the equivalent value in ms) you will get the desired date.

Instead of
var d = new Date(currentTime + daysToAdd*secondsInDay);
you can use
d.setDate(new Date().getDate()+3);

Youre problem is that the constructor of the date object uses MILISECONDS to calculate the date, and you're using SECONDS to add that 3 extra days. Instead of 86400 (seconds) you need to use the value 86400000 (miliseconds).
Goodbye!

You can add the number of days directly to d.getDate()
var d = new Date(2019, 9, 14);
var daysToAdd = 3;
var new_day = d.getDate() + daysToAdd;
var new_d = new Date(d.getFullYear(), d. getMonth(), new_day);
alert('result in Y-M-D is: ' + new_d.getFullYear() + '-' + new_d. getMonth() + '-' + new_day);

Get all mondays in the year

I always have problems figuring out dates functions
var d = new Date(),
month = d.getMonth(),
mondays = [];
d.setDate(1);
// Get the first Monday in the month
while (d.getDay() !== 1) {
d.setDate(d.getDate() + 1);
}
// Get all the other Mondays in the month
while (d.getMonth() === month) {
var pushDate = new Date(d.getTime());
mondays.push(pushDate.getDate() + '-' + (pushDate.getMonth()+1) + '-' + pushDate.getFullYear());
d.setDate(d.getDate() + 7);
}
I am using this function to get all mondays in a month, current month.
How can I adapt this code to get all remaining mondays in the year?

Just loop through the year instead of the month. The code is the same as yours, it works fine. just changed month -> year and getMonth() -> getYear()
var d = new Date(),
year = d.getYear(),
mondays = [];
d.setDate(1);
// Get the first Monday in the month
while (d.getDay() !== 1) {
d.setDate(d.getDate() + 1);
}
// Get all the other Mondays in the month
while (d.getYear() === year) {
var pushDate = new Date(d.getTime());
mondays.push(pushDate.getDate() + '-' + (pushDate.getMonth()+1) + '-' + pushDate.getFullYear());
d.setDate(d.getDate() + 7);
}

var x = new Date();
//set the financial year starting date
x.setFullYear(2016, 03, 01);
//set the next financial year starting date
var y = new Date();
y.setFullYear(2017, 03, 01);
var j = 1;
var count = 0;
//getting the all mondays in a financial year
for (var i = 0; x < y; i += j) {
if (x.getDay() === 1) {
document.write("Date : " + x.getDate() + "/" +
(x.getMonth() + 1) + "<br>");
x = new Date(x.getTime() + (7 * 24 * 60 * 60 * 1000));
j = 7;
count++;
} else {
j = 1;
x = new Date(x.getTime() + (24 * 60 * 60 * 1000));
}
}
document.write("total mondays : " + count + "<br>");

This is just an alternative, it uses a simpler method of getting the first day of the month.
// Get all Mondays in year from provided date
// Default today's date
function getMondays(d) {
// Copy d if provided
d = d ? new Date(+d) : new Date();
// Set to start of month
d.setDate(1);
// Store end year and month
var endYear = d.getFullYear() + 1;
var endMonth = d.getMonth();
// Set to first Monday
d.setDate(d.getDate() + (8 - (d.getDay() || 7)) % 7);
var mondays = [new Date(+d)];
// Create Dates for all Mondays up to end year and month
while (d.getFullYear() < endYear || d.getMonth() != endMonth) {
mondays.push(new Date(d.setDate(d.getDate() + 7)));
}
return mondays;
}
// Get all Mondays and display result
// SO console doensn't show all results
var mondays = getMondays();
mondays.forEach(function(mon) {
console.log(mon.toLocaleString(void 0, {
weekday: 'short',
day: 'numeric',
month: 'short',
year: 'numeric'
}));
});
// Count of Mondays, not all shown in SO console
console.log('There are ' + mondays.length + ' Mondays, the first is ' + mondays[0].toString())

With date-fns
https://date-fns.org/v2.28.0/docs/eachWeekOfInterval
eachWeekOfInterval({
start: new Date('2022/01/01'),
end: new Date('2022/5/31')
}, { weekStartsOn: 1 })

Formatting and Calculating dates with javascript

I'm new to javascript and I'm trying to generate a date that is:
A.) Formatted (mm/dd/yyyy)
B.) Displayed as three months later than the actual date.
I've spliced together a few things I could find and is seems to work to return the correct date, but I'm concerned it will break later in the year. Is there a better way to accomplish what I'm trying to do? The script is below, thanks in advance for the help.
<script type="text/javascript">
var dt = new Date();
var month = dt.getMonth();
var day = dt.getDate();
var year = dt.getFullYear();
if (month == 9) { var dt = new Date();
var month = dt.getMonth()-8;
var day = dt.getDate();
var year = dt.getFullYear();
var next_year = dt.getFullYear()+1;
document.write(month + '-' + day + '-' + next_year)}
else if (month == 10) { var dt = new Date();
var month = dt.getMonth()-8;
var day = dt.getDate();
var year = dt.getFullYear();
var next_year = dt.getFullYear()+1;
document.write(month + '-' + day + '-' + next_year)}
else if (month == 11) { var dt = new Date();
var month = dt.getMonth()-8;
var day = dt.getDate();
var year = dt.getFullYear();
var next_year = dt.getFullYear()+1;
document.write(month + '-' + day + '-' + next_year)}
else { var dt = new Date();
var month = dt.getMonth()+4;
var day = dt.getDate();
var year = dt.getFullYear();
document.write(month + '-' + day + '-' + year);}
</script>

The date object has methods that allows not only to set month, date and year, but get too.
function getMyDate() {
var date = new Date();
date.setMonth(date.getMonth() + 3);
return (date.getMonth() + 1) + '-' + date.getDate() + '-' + date.getFullYear();
}
document.write(getMyDate());
P.S. The scope of var is the function, not block {}. So, if you declared var dt at the top of your scope, you mustn’t use var dt in if statement. It’s a mistake.

You don't need to worry about dealing with the last three months of the year. Adding three months to a a date that causes it to 'overflow' will correctly set it to next year (eg adding three months to November 2015 will produce a date in February 2016).
var dt = new Date();
dt.setMonth(dt.getMonth() + 3);
document.write((dt.getMonth() + 1) + "-" + dt.getDate() + "-" + dt.getFullYear();
For what it's worth, your code looks correct. Just unnecessarily complex.

To print todays date you should concat the date values:
var d = new Date();
var str = (d.getMonth() + 1) + '/' + d.getDate() + '/' + d.getFullYear();
if you want to add months to your date:
var d = new Date();
var threeMonthsFromToday = new Date(new Date(d).setMonth(d.getMonth()+3));
var str = (d.getMonth() + 1) + '/' + d.getDate() + '/' + d.getFullYear();

Javascript Date Function not working

I am trying to display the text 'Oct 09, 2012'. Instead it is not running the function and is displaying a lot of unnessecary date text. Does anyone know what I am doing wrong?
You can play with my jsfiddle... http://jsfiddle.net/UP3fd/
Here is the code...
var myDate = new Date();
convertDate(myDate);
myDate.setFullYear(2012, 9, 9);
document.write(myDate);
function convertDate(d) {
var day = d.getDate();
if (day < 10) {
day = "0" + day;
}
var year = d.getFullYear();
var month = d.getMonth();
var months=["Jan","Feb","Mar","Apr","May","June","July","Aug","Sep","Oct"," Nov","Dec"];
var currentMonth = months[month];
return (currentMonth + " " + day + ", " + year);
}

You are calling your function before you set your date, and you are not saving/outputting the return value anywhere.
var myDate = new Date();
myDate.setFullYear(2012, 9, 9);
document.write( convertDate(myDate) );
function convertDate(d) {
var day = d.getDate();
if (day < 10) {
day = "0" + day;
}
var year = d.getFullYear();
var month = d.getMonth();
var months=["Jan","Feb","Mar","Apr","May","June","July","Aug","Sep","Oct"," Nov","Dec"];
var currentMonth = months[month];
return (currentMonth + " " + day + ", " + year);
}
​

var strDate = addZero(d.getDate()) + "/" + addZero((d.getMonth() + 1))+
"/" +d.getFullYear();
alert("strDate :"+strDate)
return strDate;
}
function addZero(i) {
if (i < 10) {
i = "0" + i;
}
return i;
}

This is the correct code:
var myDate = new Date();
myDate.setFullYear(2012, 9, 9);
myDate = convertDate(myDate);
document.write(myDate);
[...]

Here's the corrected code, this should return you what you are expecting.
var myDate = new Date();
myDate.setFullYear(2012, 9, 9);
var newDate = convertDate(myDate);
document.write(newDate);
function convertDate(d) {
var day = d.getDate();
if (day < 10) {
day = "0" + day;
}
var year = d.getFullYear();
var month = d.getMonth();
var months=["Jan","Feb","Mar","Apr","May","June","July","Aug","Sep","Oct"," Nov","Dec"];
var currentMonth = months[month];
return (currentMonth + " " + day + ", " + year);
}

How to get current date in jQuery?

I want to know how to use the Date() function in jQuery to get the current date in a yyyy/mm/dd format.

Date() is not part of jQuery, it is one of JavaScript's features.
See the documentation on Date object.
You can do it like that:
var d = new Date();
var month = d.getMonth()+1;
var day = d.getDate();
var output = d.getFullYear() + '/' +
(month<10 ? '0' : '') + month + '/' +
(day<10 ? '0' : '') + day;
See this jsfiddle for a proof.
The code may look like a complex one, because it must deal with months & days being represented by numbers less than 10 (meaning the strings will have one char instead of two). See this jsfiddle for comparison.

If you have jQuery UI (needed for the datepicker), this would do the trick:
$.datepicker.formatDate('yy/mm/dd', new Date());

jQuery is JavaScript. Use the Javascript Date Object.
var d = new Date();
var strDate = d.getFullYear() + "/" + (d.getMonth()+1) + "/" + d.getDate();

Using pure Javascript your can prototype your own YYYYMMDD format;
Date.prototype.yyyymmdd = function() {
var yyyy = this.getFullYear().toString();
var mm = (this.getMonth()+1).toString(); // getMonth() is zero-based
var dd = this.getDate().toString();
return yyyy + "/" + (mm[1]?mm:"0"+mm[0]) + "/" + (dd[1]?dd:"0"+dd[0]); // padding
};
var date = new Date();
console.log( date.yyyymmdd() ); // Assuming you have an open console

In JavaScript you can get the current date and time using the Date object;
var now = new Date();
This will get the local client machine time
Example for jquery LINK
If you are using jQuery DatePicker you can apply it on any textfield like this:
$( "#datepicker" ).datepicker({dateFormat:"yy/mm/dd"}).datepicker("setDate",new Date());

function GetTodayDate() {
var tdate = new Date();
var dd = tdate.getDate(); //yields day
var MM = tdate.getMonth(); //yields month
var yyyy = tdate.getFullYear(); //yields year
var currentDate= dd + "-" +( MM+1) + "-" + yyyy;
return currentDate;
}
Very handy function to use it, Enjoy. You do not require any javascript framework. it just works in with plain javascript.

I know I am Late But This Is All You Need
var date = (new Date()).toISOString().split('T')[0];
toISOString() use built function of javascript.
cd = (new Date()).toISOString().split('T')[0];
console.log(cd);
alert(cd);

Since the question is tagged as jQuery:
If you are also using jQuery UI you can use $.datepicker.formatDate():
$.datepicker.formatDate('yy/mm/dd', new Date());
See this demo.

Here is method top get current Day, Year or Month
new Date().getDate() // Get the day as a number (1-31)
new Date().getDay() // Get the weekday as a number (0-6)
new Date().getFullYear() // Get the four digit year (yyyy)
new Date().getHours() // Get the hour (0-23)
new Date().getMilliseconds() // Get the milliseconds (0-999)
new Date().getMinutes() // Get the minutes (0-59)
new Date().getMonth() // Get the month (0-11)
new Date().getSeconds() // Get the seconds (0-59)
new Date().getTime() // Get the time (milliseconds since January 1, 1970)

See this.
The $.now() method is a shorthand for the number returned by the expression (new Date).getTime().

Moment.js makes it quite easy:
moment().format("YYYY/MM/DD")

this object set zero, when element has only one symbol:
function addZero(i) {
if (i < 10) {
i = "0" + i;
}
return i;
}
This object set actual full time, hour and date:
function getActualFullDate() {
var d = new Date();
var day = addZero(d.getDate());
var month = addZero(d.getMonth()+1);
var year = addZero(d.getFullYear());
var h = addZero(d.getHours());
var m = addZero(d.getMinutes());
var s = addZero(d.getSeconds());
return day + ". " + month + ". " + year + " (" + h + ":" + m + ")";
}
function getActualHour() {
var d = new Date();
var h = addZero(d.getHours());
var m = addZero(d.getMinutes());
var s = addZero(d.getSeconds());
return h + ":" + m + ":" + s;
}
function getActualDate() {
var d = new Date();
var day = addZero(d.getDate());
var month = addZero(d.getMonth()+1);
var year = addZero(d.getFullYear());
return day + ". " + month + ". " + year;
}
HTML:
<span id='full'>a</span>
<br>
<span id='hour'>b</span>
<br>
<span id='date'>c</span>
JQUERY VIEW:
$(document).ready(function(){
$("#full").html(getActualFullDate());
$("#hour").html(getActualHour());
$("#date").html(getActualDate());
});
EXAMPLE

//convert month to 2 digits<p>
var twoDigitMonth = ((fullDate.getMonth().length+1) === 1)? (fullDate.getMonth()+1) : '0' + (fullDate.getMonth()+1);
var currentDate = fullDate.getFullYear()+ "/" + twoDigitMonth + "/" + fullDate.getDate();
console.log(currentDate);<br>
//2011/05/19

You can achieve this with moment.js as well.
Include moment.js in your html.
<script src="moment.js"></script>
And use below code in script file to get formatted date.
moment(new Date(),"YYYY-MM-DD").utcOffset(0, true).format();

FYI - getDay() will give you the day of the week... ie: if today is Thursday, it will return the number 4 (being the 4th day of the week).
To get a proper day of the month, use getDate().
My example below... (also a string padding function to give a leading 0 on single time elements. (eg: 10:4:34 => 10:04:35)
function strpad00(s)
{
s = s + '';
if (s.length === 1) s = '0'+s;
return s;
}
var currentdate = new Date();
var datetime = currentdate.getDate()
+ "/" + strpad00((currentdate.getMonth()+1))
+ "/" + currentdate.getFullYear()
+ " # "
+ currentdate.getHours() + ":"
+ strpad00(currentdate.getMinutes()) + ":"
+ strpad00(currentdate.getSeconds());
Example output: 31/12/2013 # 10:07:49If using getDay(), the output would be 4/12/2013 # 10:07:49

This will give you current date string
var today = new Date().toISOString().split('T')[0];

Try this....
var d = new Date();
alert(d.getFullYear()+'/'+(d.getMonth()+1)+'/'+d.getDate());
getMonth() return month 0 to 11 so we would like to add 1 for accurate month
Reference by : https://www.w3schools.com/jsref/jsref_obj_date.asp

you can use this code:
var nowDate = new Date();
var nowDay = ((nowDate.getDate().toString().length) == 1) ? '0'+(nowDate.getDate()) : (nowDate.getDate());
var nowMonth = ((nowDate.getMonth().toString().length) == 1) ? '0'+(nowDate.getMonth()+1) : (nowDate.getMonth()+1);
var nowYear = nowDate.getFullYear();
var formatDate = nowDay + "." + nowMonth + "." + nowYear;
you can find a working demo here

var d = new Date();
var today = d.getFullYear() + '/' + ('0'+(d.getMonth()+1)).slice(-2) + '/' + ('0'+d.getDate()).slice(-2);

The jQuery plugin page is down. So manually:
function strpad00(s)
{
s = s + '';
if (s.length === 1) s = '0'+s;
return s;
}
var now = new Date();
var currentDate = now.getFullYear()+ "/" + strpad00(now.getMonth()+1) + "/" + strpad00(now.getDate());
console.log(currentDate );

console.log($.datepicker.formatDate('yy/mm/dd', new Date()));

Using the jQuery-ui datepicker, it has a handy date conversion routine built in so you can format dates:
var my_date_string = $.datepicker.formatDate( "yy-mm-dd", new Date() );
Simple.

This is what I came up with using only jQuery. It's just a matter of putting the pieces together.
//Gather date information from local system
var ThisMonth = new Date().getMonth() + 1;
var ThisDay = new Date().getDate();
var ThisYear = new Date().getFullYear();
var ThisDate = ThisMonth.toString() + "/" + ThisDay.toString() + "/" + ThisYear.toString();
//Gather time information from local system
var ThisHour = new Date().getHours();
var ThisMinute = new Date().getMinutes();
var ThisTime = ThisHour.toString() + ":" + ThisMinute.toString();
//Concatenate date and time for date-time stamp
var ThisDateTime = ThisDate + " " + ThisTime;

You can do this:
var now = new Date();
dateFormat(now, "dddd, mmmm dS, yyyy, h:MM:ss TT");
// Saturday, June 9th, 2007, 5:46:21 PM
OR Something like
var dateObj = new Date();
var month = dateObj.getUTCMonth();
var day = dateObj.getUTCDate();
var year = dateObj.getUTCFullYear();
var newdate = month + "/" + day + "/" + year;
alert(newdate);

var d = new Date();
var month = d.getMonth() + 1;
var day = d.getDate();
var year = d.getYear();
var today = (day<10?'0':'')+ day + '/' +(month<10?'0':'')+ month + '/' + year;
alert(today);

I just wanted to share a timestamp prototype I made using Pierre's idea. Not enough points to comment :(
// US common date timestamp
Date.prototype.timestamp = function() {
var yyyy = this.getFullYear().toString();
var mm = (this.getMonth()+1).toString(); // getMonth() is zero-based
var dd = this.getDate().toString();
var h = this.getHours().toString();
var m = this.getMinutes().toString();
var s = this.getSeconds().toString();
return (mm[1]?mm:"0"+mm[0]) + "/" + (dd[1]?dd:"0"+dd[0]) + "/" + yyyy + " - " + ((h > 12) ? h-12 : h) + ":" + m + ":" + s;
};
d = new Date();
var timestamp = d.timestamp();
// 10/12/2013 - 2:04:19

Get current Date format dd/mm/yyyy
Here is the code:
var fullDate = new Date();
var twoDigitMonth = ((fullDate.getMonth().toString().length) == 1)? '0'+(fullDate.getMonth()+1) : (fullDate.getMonth()+1);
var twoDigitDate = ((fullDate.getDate().toString().length) == 1)? '0'+(fullDate.getDate()) : (fullDate.getDate());
var currentDate = twoDigitDate + "/" + twoDigitMonth + "/" + fullDate.getFullYear();
alert(currentDate);

function createDate() {
var date = new Date(),
yr = date.getFullYear(),
month = date.getMonth()+1,
day = date.getDate(),
todayDate = yr + '-' + month + '-' + day;
console.log("Today date is :" + todayDate);

You can add an extension method to javascript.
Date.prototype.today = function () {
return ((this.getDate() < 10) ? "0" : "") + this.getDate() + "/" + (((this.getMonth() + 1) < 10) ? "0" : "") + (this.getMonth() + 1) + "/" + this.getFullYear();
}

This one-liner will give you YYYY-MM-DD:
new Date().toISOString().substr(0, 10)
'2022-06-09'