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When converting date, I get previous day

I want to convert a string into a date "as it is".
const date = "8/16/2019"
console.log(new Date(date))
However, I get:
As you can see I get the prevous day. I was thinking that it might be a timezone issue, even though there is no timezone that I am converting it from.
Any suggestions how to convert is as it is?
I appreciate you replies!

If your format is consistent, you could split on / and use Date.UTC. Creating your new Date from that would ensure it's UTC.
const date = "8/16/2019"
const [month,day,year] = date.split("/");
const utcDate = Date.UTC(year,month-1,day);
console.log(new Date(utcDate));

const date = "8/16/2019"
console.log(new Date(date).toLocaleString("en-US", {timeZone: "Asia/kolkata"}))
Note:- You need to add timezone

You can use toLocaleDateString
console.log(new Date("8/16/2019").toLocaleDateString('en-us', {timeZone: "Asia/Kolkata"}))

new Date("8/16/2019") will create a date object using your current timezone. Add a "Z" at the end if you want your date to be in UTC.
console.log(new Date("8/16/2019Z"))
EDIT
It appears that Firefox is not implementing the parsing of standard date format. Unfortunately until recently how exactly was a date parsed was completeley based on heuristics and intrinsically non portable.
Looking at Firefox bug tracker seems the issue has been discussed but the problem is still present (some toolkit just works around by replacing "Z" with "+00:00" before calling the parser).
The only way to be sure on every browser is to parse the string yourself and build the date from the fields. I didn't notice because I'm using chrome instead (in both chrome and Node works as expected).
EDIT 2
After more investigation seems the standard requires that:
If you use yyyy-mm-ddThh:mm:ssz then you get what ISO format for datetime defines it to be. Also the syntax described in the standard is not very precise and for example is not clear to me if the time zone can be present when no time is present (Chrome says yes, Firefox says no).
If you use another format then anything goes (so for example there is no string that is guaranteed to issue an invalid date response).
In other words new Date("8/16/2019") is not portable Javascript (with the meaning that you don't know what date / time / timezone you will get, if any). Either you parse yourself the date or you just live with what that version of that Javascript engine in that moment decides to give you.

Check if start datetime and end datetime are valid in momentjs

Im new to momentJs so I need a bit of help here. I am building a form where the user can send in their availabilities for a certain work period. So in the form you have a startDate, startTime, endDate and endTime. Due to the api that I have to use from a client we have to send the date like this (example) "2015-06-17T14:24:36" (with the 'T' in the middle). Currently I receive the date and the time seperate from eachother but merging them together in the end so it fits the api's way of reading date.
Now my question is as follow. I have to create a check where I can see if the input startdate-time and enddate-time are valid. For example the startdate always has to be a date BEFORE the end date (pretty logic right). But is there an easy way to do this in momentJS?
Or should I use another method?
Thanks in regard and if my question is not quite clear please let me know so I can provide extra information!
NOTE: in the end it should be something like this:
var start = "2017-06-17T14:24:36"
var end = "2017-07-03T14:24:36"
Function that checks if the start and end dates are valid
Result = true

If you simply have to check that startDate is before endDate you can use isAfter.
Here a working sample:
var start = "2017-06-17T14:24:36";
var end = "2017-07-03T14:24:36";
function checkDate(start, end){
var mStart = moment(start);
var mEnd = moment(end);
return mStart.isBefore(mEnd);
}
console.log(checkDate(start, end));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
In my first example I'm using moment(String) parsing that accepts input in ISO 8601 format.
If you need to parse non ISO 8601 format you can use moment(String, String) specifying input format (e.g. var mStart = moment(start, 'DD-MM-YYYYTHH:mm:ss');).
If you have to support multiple formats you can use moment(String, String[]). As docs states moment(String, String[]):
Prefer formats resulting in valid dates over invalid ones.
Prefer formats that parse more of the string than less and use more of the format than less, i.e. prefer stricter parsing.
Prefer formats earlier in the array than later.

datejs overwriting Date in javascript

I am using date js to quickly parse any string into a date and it is working perfectly. However I need to also parse a timestamp.
var temp_string = "1484120122526";
var date = new Date(temp_string);
It gives back
NaN –
Regular javascript Date object does this, but I can't find a way for datejs to do it. And since it overwrites the Date object, I am stuck. Can datejs parse timestamps? or is there a way for me to call new Date() and reference the original date object?

Even though dateJS does indeed overwrite the default js Date class, the fault was on my side, I did not see in the documentation the fact that timestamp has to be an int, as I was looking everywhere in the dateJS documentation not the Date one.
so the code should be:
var temp_int = 1484120122526;
var date = new Date(temp_int);

8601 ISO String to readable date format in Javascript

I'm having a pretty horrid time trying to convert an 8601 into a readable format. The date shows as 'P0DT0H0M10S' and is stored in a var called timeLeft. Every article I find online tells me how to turn dates INTO the 8601 format, but not the other way around.
I tried using moment.js but that seems to revolve around the current date and not one set by my timeLeft var. How do I get this var into a user-friendly format? Thanks

Moment has a duration type:
var duration = moment.duration('P1Y2M3DT4H5M6S');
// user-friendly format
var out = duration.humanize();
snippet.log(out);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.11.1/moment.min.js"></script>
<script src="https://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

First off, that's not an ISO-8601 date (not even close).
Second, momentjs does support parsing a string into a moment, with the moment("20111031", "YYYYMMDD") syntax (from their front page examples).
I'm not sure what the pattern you need would be, but maybe something like [P]D[DT]H[H]M[M]S[S].

Getting the proper date from forms that are day/month/year

When writing a new date object with a string, one can write it as:
var someDay = new Date("12/01/2012");
This equals December 1st 2012.
However, what if the user has to fill in a date on a website where the format isn't month/day/year, but day/month/year? How would one go about creating a date object with the correct date then?

If you are getting the data as a string from another website, then you need to know the format in which that website provides you the date. There is no way around this because D-M-Y and M-D-Y are indistinguishable; even Y-M-D would be indistinguishable if they used a two-digit format for the year.
This hasn't been tested at all, but at worst the general idea should solve your problem.
var pattern = /^(\d+)\b(\d+)\b(\d+)$/;
if (!pattern.test(dateString))
return null;
var matches = dateString.match(pattern);
if (siteUsesDMY)
return new Date(matches[2], matches[1]-1, matches[0]);
if (siteUsesMDY)
return new Date(matches[2], matches[0]-1, matches[1]);
...
Pattern: This pattern supports any numeric representation of the date, assuming it has a breaking character between each unit. If you need to support a website that doesn't have a breaking character, you would need a different pattern that matched that website's exact format (i.e.: site sends DDMMYYYY, then pattern would be /^(\d{2})(\d{2})(\d{4})$/).
Also fixed the month parameter in date creation, as I just remembered that JavaScript uses 0-11 for months.