Develop Reference

How to get difference in dates between to dates in JavaScript

I have a split string lines="Ram Hue, 134, 20.5.1994, 20.4.2004"
and I want to get the difference in dates between to dates 20.5.1994 and 20.5.1994, I tried in JavScript but i'ts not working. Also when trying to extract both dates using
lines[2] lines[3] I'm getting wrong outputs
var date1 = new Date(lines[2])
var date2 = new Date(lines[3])
var diffDays = parseInt((date2-date1)/(1000*60*60*24),10)
console.log(diffDays)

Since lines is a string, lines[2] will just get you the character with index 2 within the string. Instead you need to split the string before:
const arr = lines.split(',');
Then you can access both date strings as arr[2] and arr[3]

Date in variable reading as "Invalid Date"

Using the following:
var timestart = $('.thisDiv').data("timestart");
var startDateTime = new Date(timestart);
to collect a date from a php file that is updating by ajax from this:
$TimeStart = date( 'Y,m,d,g,i', $TimeStart );
<div class="thisDiv" data-timestart="<?= $TimeStart ?>"></div>
var timestart = $('.thisDiv').data("timestart");
In console I'm getting the following when logging timestart and startDateTime:
2017,07,24,7,50
Invalid Date
If I paste the date that is output as follows
var startDateTime = new Date(2017,07,24,7,50);
Then it works fine. Any ideas why I'm getting Invalid Date?

Your timestart variable (JavaScript) is just a string. So it's a string 2017,07,24,7,50, and not those elements in order - which can't be used as separate parameters like new Date() expects.
Let's take a look at it!
var startDateTime = new Date(2017,07,24,7,50); // Parameters in order - all OK!
var startDateTime = new Date("2017,07,24,7,50"); // A single string - single parameter, not OK!
You need to return a proper format of dates from PHP with a format that's valid in JavaScript. Per the ECMAScript standard, the valid format that should work across all browsers is YYYY-MM-DDTHH:mm:ss.sssZ (see the reference at the bottom). To define that from PHP, you would need to format it as such
$TimeStart = date('c', $TimeStart);
This would return a format such as 2017-07-24T21:08:32+02:00.
Alternatively, you can use a splat/spread-operator ... and split the string it into elements, which I find as the better approach than above.
var timestart = $('.thisDiv').data("timestart"); // Get the string: "2017,07,24,7,50"
timestart = timestart.split(","); // Split into array
var startDateTime = new Date(...timestart); // Pass as arguments with splat-operator
Spread/splat operator in JavaScript
PHP date() documentation
ECMAScript date string (JavaScript)

You need to convert your date from string format to numbers.
var timestart = $('.thisDiv').data("timestart").split(",").map(Number);
var startDateTime = new Date(...timestart);
console.log(startDateTime)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="thisDiv" data-timestart="2017,07,24,7,50"></div>

Time if statement not working

Hi I have a simple if statement which compares to dates, however its not running, I have tried debugging it but doesn't work.
dateFormat = "01/05/2099"
dateMissing = "25/11/2016"
if(dateFormat > dateMissing){
dateFormat = dateMissing;
}

You're comparing strings. That compares their characters, one by one from left-to-right, until it finds a difference, and then uses that difference as the result. Since "2" is > "0", that string is greater than the other.
You need to parse the dates and compare the result. Do not just use new Date(dateFormat) or similar, those strings are not in a format that is handled by JavaScript's Date object. Do the parsing yourself (directly, or via a library). E.g.
var dateFormat = "01/05/2099";
var dateMissing = "25/11/2016";
var parts, dt1, dt2;
var parts = dateFormat.split("/");
var dt1 = new Date(+parts[2], +parts[1] - 1, +parts[0]);
parts = dateMissing.split("/");
var dt2 = new Date(+parts[2], +parts[1] - 1, +parts[0]);
if (dt1 > dt2) {
dateFormat = dateMissing;
}
console.log("dateFormat:", dateFormat);
console.log("dt1", dt1.toString());
console.log("dt2", dt2.toString());

Your can't simply compare the strings containing dates. First, convert them to an acceptable format (milliseconds).
var dateFormat = new Date("05/01/2099").getTime();
var dateMissing = new Date("11/25/2016").getTime();
Then you can do your date comparision.

Google forms to calendar event issues with date format

So I have a very simple form that takes 3 inputs, a title, start and end date. I have tried to use a simple script to produce a calendar event. this can be seen below.
function onFormSubmit(e) {
var title = e.values[1];
var start_time = new Date(e.values[2]);
var end_time = new Date(e.values[3]);
CalendarApp.createEvent(title, start_time, end_time);
}
The issue I have is that as the date string is UK format (e.g. 05/12/2016 12:00:00) it is logging the events as 12th May as opposed to 5th December.
I am new to all of this so am looking for an elegant and simple solution I understand, not just to copy code I don't.
Thanks.

function convertUKDateToUSDate(date) {
const arr = date.split('/');
const temp = arr[0];
arr[0] = arr[1];
arr[1] = temp;
return arr.join('/');
}
will convert a date string with the prefix "DD/MM/" into "MM/DD/YYYY" format. Split turns the string into an array like ["DD", "MM", "YYYY HH:MM:SS"] and then the temporary variable is used to swap the "MM" and "DD" before the array entries are joined back together with the same character that was used to split them. You'll end up with a final onFormSubmit(e) like this:
function onFormSubmit(e) {
var title = e.values[1];
var start_time = new Date(convertUKDateToUSDate(e.values[2]));
var end_time = new Date(convertUKDateToUSDate(e.values[3]));
CalendarApp.createEvent(title, start_time, end_time);
}
Obviously I'm assuming e.values[2] and e.values[3] are strings. If they're Date objects already (or if you just want a shorter solution), then consider using the Moment.js (the premier Date object library) format function to convert between the formats. Normally I'd recommend using Moment anyways but you said you wanted something you could understand instead of copy.

Javascript convert dates

I am getting this "20131218" date/time value from an API result.
What I want to do is convert this date into something like this "2013-12-18". I know this is very easy in PHP by simply doing this code:
echo date("Y-m-d",strtotime('20131218'));
output: 2013-12-18
This is what I tried in javascript:
var myDate = new Date("20131218");
console.log(myDate);
But the output is Date{ Invalid Date } so obviously this is wrong.
My question here what is the equivalent of strtotime in javascript? or if there's no equivalent, how would I convert this value as my expected result(2013-12-18) using javascript?
Your help will be greatly appreciated!
Thanks! :)

The value is invalid to convert it to date. So either from your PHP code send it as a proper format like 20131218
Or convert the value you get in your Javascript to similar kind of format.
var dateVal="20131218";
/*
// If it's number ******* //
var numdate=20131218;
var dateVal=numdate.toString();
*/
var year=dateVal.substring(0,4);
var mnth=dateVal.substring(4,6);
var day=dateVal.substring(6,8);
var dateString=year+"-"+mnth+"-"+day;
var actualDate = new Date(dateString);
alert(actualDate);
JSFIDDLE DEMO

Javascript has a Date.parse method but the string you have is not suitable to pass to it. You don't really need to create a date object just to format a string. Consider:
function formatDateStr(s) {
s = s.match(/\d\d/g);
return s[0] + s[1] + '-' + s[2] + '-' + s[3];
}
alert(formatDateStr('20131218')); // '2013-12-18'
If you wish to convert it to a date object, then:
function parseDateStr(s) {
s = s.match(/\d\d/g);
return new Date(s[0] + s[1], --s[2], s[3]);
}

The reason why it is showing Invalid date is, it wants it to be in format
Following format: YYYY-MM-DD or YYYY-MM-DDTHH:MM:SS
If you breakdown your string using following format just add dash at relevant places then you are good to go and use newDate.
1. var myDate = new Date("2013-12-18");
alert(myDate);
2. var myDate = new Date(2013,12,18);
Eventually you can modify your string manipulate it and use it in aforementioned format.