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show certain date in date picker

I'm using pickmeup datePicker in my Angular project, and it works good and stable but I faced a problem. When I'm trying to set a particular date, picker breaks and/or disappears. I used the method set_date from the documentation but I think I'm missing something.
I use the following code
showDate(timestamp: number) {
const timeString = timestamp.toString();
this.pickerInstance.set_date(new Date(timeString));
}
I have a stackblitz code template here.
So the idea is, I want to have a button when I'm pressing on it, it passes timestamp value to showDate function and after that datePicker shows my date.
I don't want to use jquery here, I believe this could be done without it. But maybe I'm wrong.
Any ideas, comments, help is welcome? thank you.

The constructor of Date needs a number not a a string.
You need to call this.pickerInstance.update() after the update
public showDate(timestamp: number) {
this.pickerInstance.set_date(new Date(timestamp));
this.pickerInstance.update();
}

How to deal with gregorian and julian dates form

I'm kinda new to Javascript.
My problem is the following : I have to implement a form that is generated by a js file, by taking the url and paste it inside my HTML. I have a date input, and I need to verify if the date is right, wether it is dd/mm/aaaa or mm/dd/aaaa.
If possible, without using regExp. I already made this function out of StackOverflow RegExp :
function validateDateRegExp(field){
var date=field.value;
var regExp1 = /^(((0[1-9]|[12]\d|3[01])[\s\.\-\/](0[13578]|1[02])[\s\.\-\/]((19|[2-9]\d)\d{2}))|((0[1-9]|[12]\d|30)[\s\.\-\/](0[13456789]|1[012])[\s\.\-\/]((19|[2-9]\d)\d{2}))|((0[1-9]|1\d|2[0-8])[\s\.\-\/]02[\s\.\-\/]((19|[2-9]\d)\d{2}))|(29[\s\.\-\/]02[\s\.\-\/]((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/;
var regExp2 = /^((\d{2}(([02468][048])|([13579][26]))[\-\/\s]?((((0?[13578])|(1[02]))[\-\/\s]?((0?[1-9])|([1-2][0-9])|(3[01])))|(((0?[469])|(11))[\-\/\s]?((0?[1-9])|([1-2][0-9])|(30)))|(0?2[\-\/\s]?((0?[1-9])|([1-2][0-9])))))|(\d{2}(([02468][1235679])|([13579][01345789]))[\-\/\s]?((((0?[13578])|(1[02]))[\-\/\s]?((0?[1-9])|([1-2][0-9])|(3[01])))|(((0?[469])|(11))[\-\/\s]?((0?[1-9])|([1-2][0-9])|(30)))|(0?2[\-\/\s]?((0?[1-9])|(1[0-9])|(2[0-8]))))))(\s(((0?[1-9])|(1[0-2]))\:([0-5][0-9])((\s)|(\:([0-5][0-9])\s))([AM|PM|am|pm]{2,2})))?$/;
if(!(regExp1.test(date)||regExp2.test(date))){
alert(date);
document.getElementById('fld_CS_BuyingDate').value="";
}
}
I'm looking for a solution since 2 days, but the answers are not clear, or the problem is not the same.
Does anyone have any idea on how I could work that out ?
Thanks for the future answers

Very custom date format in momentjs

I am working with kibana (elasticsearch dashboard) which allow to specify a date pattern to explain the index naming pattern.
For instance, default pattern is: [logstash-]YYYY-MM-DD.HH
I'd like to organize my index by block of hours, let's say by block of 4 hours. Indices would then be named logstash-2014-02-25.00, logstash-2014-02-25.04, logstash-2014-02-25.08, …
Is there any way to get such format with momentjs ? I am dreaming of [logstash-]YYYY-MM-DD.{HH%4}
but the documentation does not explain such thing (how weird).

It seems impossible to do it with formatting primitives.
However, I found we can override some of the language-dependant formatter such as meridiem formatter.
A solution would then be to insert somewhere (in kibana conf file for example):
moment.lang('fourHourblocks', {
meridiem: function(hour, minute, isLowercase) {
hourBlock = Math.floor(hour / 4).toString();
if (hourBlock.length < 2) hourBlock = "0" + hourBlock;
return hourBlock;
}
}
then I can set the pattern to [logstash-]YYYY-MM-DD.A.
This is kind of hacky so I am still opened to other solutions

Calculate date difference in jQuery

The question is; there are 2 fields in my application, one is date (Field1) and second is a label (Field2). So, I want that when user selects a date in field 1, then field 2 should be automatically populated (current date - date from field 1).
Can anyone help on how to implement it.
I'm using jQuery to display date:
// This displays the date dialog when user clicks on Field1
$('#Field1').click(function () {
$('#Field1').simpleDatepicker();
});
// Tried following code but it didn't worked
$('#Field1').click(function () {
$('#Field1').simpleDatepicker({
onSelect: function () {
$('#Field2').value(calculateDays($('#Field1').toString))
}
});
});
function calculateDays(dateString) {
var today = new Date();
var inputDate = new Date(dateString);
var days = today - inputDate;
return days;
};
This may look like pathetic code to some folks but I'm just a beginner, so any suggestions/comments are welcome.
Also please tell me if this can be done using html only and no need to go to jQuery. It is my understanding that the calculating days (difference between dates) code will go in jQuery since this needs to be fired after selecting date ('onSelect' event). Please correct if wrong.

I'm assuming that you're trying to use Karl Seguin's jquery.simpleDatePicker (it came top when searching for "simpledatepicker" on Google).
As Jimbo remarks in the comments, it's hard to advise on an MVC approach here — you say you want to do this purely with HTML, but HTML alone can't dictate behaviour (I'd say that's extremely un-MVC). HTML5 forms do allow some limited behavioural control (validation etc), and they also offer <input type="date"/>, but none of these help your situation.
So for this answer I'm just going to fix the mistakes in your code:
The plugin is initialised with the simpleDatePicker jQuery method — you forgot to capitalise the 'P';
The plugin itself caters for the click event. You should initialise it directly without waiting for user input;
There was no onSelect initialisation option in the source code: I chose to use a change event listener on the input to capture this;
You use the jQuery method value — that's native DOM Javascript — you should be using val instead;
toString won't work on DOM elements or jQuery objects — again, use the val method;
The native Date object can't parse dates in arbitrary formats — nor would your code produce a number of days if it did (it would just produce the difference in milliseconds). For this kind of functionality you should use a good date library: I've opted for Moment.
Resulting code (as demonstrated here):
$('#Field1')
.simpleDatePicker()
.on('change', function passValue(){
$('#Field2').val(calculateDaysFromNow($('#Field1').val()))
});
function calculateDaysFromNow(dateString){
return moment.duration(moment(dateString,'MMM DD YYYY').diff()).days();
}
A bit of elaboration on how I've used moment:
First of all, we want to parse #Field1's formatted date for an actual quantifiable date object:
moment(dateString,'MMM DD YYYY')
Next, we want to differentiate that from now. Like Date, moment assumes now if we pass no argument:
moment(dateString,'MMM DD YYYY').diff()
We don't want this as a date, but as a duration, so we'll pass it to moment's duration method:
moment.duration(moment(dateString,'MMM DD YYYY').diff())
…and finally, we want this expressed in days:
moment.duration(moment(dateString,'MMM DD YYYY').diff()).days()

I'm not sure but this:
$('#Field2').value(calculateDays($('#Field1').toString)) should be like this:
$('#Field2').value(calculateDays($('#Field1').val())) or $('#Field2').value(calculateDays($('#Field1').text()))

Here is solution for setting same date in second field.
Link:jquery: using two datepicker with two fields ( field 1 , field2 + 1 day ) like booking.com
Change the format according to your need.

Parse ONLY a time string with DateJS

I'm using the excellent (but large) DateJS library to handle dates and times in my webapp. I just came across something that I'm not sure how to handle.
I want my users to be able to enter Time strings only, without a date, but they should be able to enter it in any manner they please. For instance:
5:00 pm
17:00
5:00pm
5:00p
5p
etc.
Using Date.parse(value) converts these strings into a full date, which is exactly what I want. However, it also allows the user to enter any other part of a date string, such as:
sat 5pm
1/1/2010 5pm
etc.
I'm trying to use DateJS to validate an input field for a time value. Something like:
function validateTime(value) {
return Date.parse(value) !== null;
}
Is there a way to use DateJS features to solve this? There are other SO questions that provide solutions, but if DateJS has a way to do this, I don't really want to add more custom code to my app to do this.

Shortly after asking my question, I discovered that Date.parseExact() can take an array of format strings. Somehow I'm missed that. I managed to get something working with the following code:
function validateTime(input) {
return Date.parseExact(input, [
"H:m",
"h:mt",
"h:m t",
"ht","h t"]) != null ||
Date.parseExact(input, [
"h:mtt",
"h:m tt",
"htt","h tt"]) != null;
};
Note that some formats don't seem to be able to be included together at the same time, which is why I split them into two separate parseExact() calls. In this case, I couldn't include any string that contained a single t in it with format strings that contained a double tt in it.

The additive approach seems cumbersome. Takes away the beauty of DateJS in my opinion. I needed the same solution and decided to just sneakily append the date in front of my input string before parsing with DateJS:
var parsed = Date.parse(Date.today().toString('M/d/yyyy') + ' ' + this.value);
if (parsed) {
alert(parsed.toString('h:mm tt'));
}
Now DateJS will not be sniffing around for any of its date-part parsing patterns, as you have already subbed it in.
Hope this helps someone!