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How to set time with AM PM in Javascript Date Object

Say that I have DateTime in this format Fri Feb 02 2018 00:00:00 GMT+0530 (IST)
And from the time picker plugin getting the time 1:10am or 2:30pm in this format.
I am not sure how to calculate and combine/add them both to produce this result:
Fri Feb 02 2018 01:10:00 GMT+0530 (IST) or Fri Feb 02 2018 14:30:00 GMT+0530 (IST)
I wish if there was something to do as simple as this:
new Date(dateString).setHours(1:10am)

Seems like you need to parse it on your own:
function parseDaytime(time) {
let [hours, minutes] = time.substr(0, time.length -2).split(":").map(Number);
if (time.includes("pm") && hours !== 12) hours += 12;
return 1000/*ms*/ * 60/*s*/ * (hours * 60 + minutes);
}
To add it to a date:
new Date(
+new Date("Fri Feb 02 2018 00:00:00 GMT+0530")
+parseDaytime("1:20pm")
);

Here is a simple function to do what your after.
It basically splits the time using a regex, and then calls setHours & setMins, adding 12 hours if pm is selected.
The example below takes the current datetime, and sets 1:10am & 2:40pm..
function setHours(dt, h) {
var s = /(\d+):(\d+)(.+)/.exec(h);
dt.setHours(s[3] === "pm" ?
12 + parseInt(s[1], 10) :
parseInt(s[1], 10));
dt.setMinutes(parseInt(s[2],10));
}
var d = new Date();
console.log(d);
setHours(d, "1:10am");
console.log(d);
setHours(d, "2:40pm");
console.log(d);

You can parse the time string into hours & minutes, adjust the hours according to am/pm & set it to the date object then:
var dateString = 'Fri Feb 02 2018 00:00:00 GMT+0530 (IST)';
var hoursString = '2:30pm';
var parts = hoursString.replace(/am|pm/, '').split(':')
var hours = parseInt(parts[0]) + (hoursString.indexOf('pm') !== -1 ? 12 : 0);
var minutes = parts[1];
var date = new Date(dateString);
date.setUTCHours(hours, minutes);
console.log(date); // in your local time
console.log(date.toUTCString()); // in UTC (i.e. without timezone offset)
(Note setHours / setUTCHours mutates date object but returns unix timestamp of the updated datetime.)

Comparision between two dates

I have a calender and has following two scenarios:
case - 1
current_month = 8 (aug)
end_month = 10 (oct)
current_year = 2017
end_year = 2017
case - 2
current_month = 8 (aug)
end_month = 2 (feb)
current_year = 2017
end_year = 2018
When I click next month it should move only until "end_month". What should be the condition to satisfy both the cases:
if(condition)
alert("Move to next month");
else
alert("condition fail");
I have tried comparing start and end date objects, But I'm able to move one more month extra, which should not happen.
I have used the following conditions:
cal_date = Tue Aug 01 2017 23:58:33 GMT+0530 (India Standard Time)
$scope.edate = Wed Nov 15 2017 00:00:00 GMT+0530 (India Standard Time)
if (cal_date.getMonth() > $scope.edate.getMonth() + 1 || cal_date.getMonth() == $scope.edate.getMonth() || $scope.edate.getFullYear() <= new Date().getFullYear())
if (cal_date.getMonth() > $scope.edate.getMonth() || cal_date.getMonth() == $scope.edate.getMonth())
if (cal_date.getTime() < new Date(new Date($scope.edate) - 1)) {
if (cal_date < $scope.edate) {

Personally I would create Date objects:
var current = new Date(year,month)
var end = new Date(year,month)
and then test:
if ( current<end )
That would probably be the simplest approach.

Get Meridian from time in Javascript

I have following time "Mon Jun 22 03:45:24 PDT 2015" how can I get Meridian using Javascript.
I was doing this:
d= Mon Jun 22 03:45:24 PDT 2015;
var hours = d.getHours();
var meridiem = "AM";
if (d.getHours() > 12) {
hours = d.getHours() % 12;
if (hours == 2) {
hours = 12;
}
meridiem = "PM";
}
But its not working in IE 8.

you define
d= Mon Jun 22 03:45:24 PDT 2015;
actually it is nothing in javascript
some browser more intelligent some not, it's up to the browser behaviour
you have to tell javascript like that
function getCurrentTime() {
var currentTime;
// here we can give our date
var currentDate = new Date("Mon Jun 22 03:45:24 PDT 2015");
// OR we can define like that also for current date
// var currentDate = new Date();
var hour = currentDate.getHours();
var meridiem = hour >= 12 ? "PM" : "AM";
currentTime = ((hour + 11) % 12 + 1) + ":" + currentDate.getMinutes() + meridiem;
return currentTime;
}

We can get time in 12 hour format, including the meridian by using the Date.prototype.toLocaleTimeString() method with a US English argument which returns the time in AM/PM. Without the argument 'en-US' date will return the format it deems appropriate for your timezone.
From there we can utilise the slice method to get the last two characters of the timestamp using a negative index:
var d = new Date("Mon Jun 22 03:45:24 PDT 2015")
// US English uses 12-hour time with AM/PM
var timestamp = d.toLocaleTimeString('en-US');
// timestamp → "03:45:24 AM"
var meridian = timestamp.slice(-2);
// meridian → "AM"
One liner for brevity:
var meridian = new Date("Mon Jun 22 03:45:24 PDT 2015").toLocaleTimeString().slice(-2);

According to the documentation for JavaScript Date object here, there is no method for directly getting 12-hour hours and therefore no method for getting am/pm directly from the Date object.
You can get hours (24-hour format) which you can use to get 12-hour hours and am/pm. (You've already done it but I don't understand what you're trying to do in your code.)
This would be one way to do this.
This code is inspired by #tinka.
var d = new Date("Mon Jun 22 03:45:24 PDT 2015");
var h = (d.getHours() + 11) % 12 + 1; //Courtesy #tinka
var m = h > 12 ? 'pm' : 'am';
And you can always add methods to Date.prototype if you're gonna be using them repeatedly.
Date.prototype.getHours12 = function() {
return (this.getHours() + 11) % 12 + 1; // edited.
}
Date.prototype.getMeridiem = function() {
return this.getHours() > 12 ? 'pm' : 'am';
}
It should work on all platforms.

With Date object:
getMeridiem(date: Date) {
return date.toLocaleTimeString().split(' ')[1];
}

Date.UTC() returns last day of previous month while getUTCFullYear(), getUTCMonth() returns correctly first day of correct month

I'm getting a strange result:
var date = new Date();
var year = date.getMonth() < 11 ? date.getFullYear() : date.getFullYear() + 1;
var month = date.getMonth() < 11 ? date.getMonth() + 1 : 0;
console.log(new Date(Date.UTC(year, month)));
var utcYear = date.getUTCMonth() < 11 ? date.getUTCFullYear() : date.getUTCFullYear() + 1;
var utcMonth = date.getUTCMonth() < 11 ? date.getUTCMonth() + 1 : 0;
console.log(new Date(utcYear, utcMonth));
With the particular date I'm using (any date will do), Date.UTC gives me:
Sun May 31 2015 19:00:00 GMT-0500 (Central Daylight Time)
The getUTC... aproach gives me:
Mon Jun 01 2015 00:00:00 GMT-0500 (Central Daylight Time)
Am I mis-using Date.UTC or am I missing something?
Thanks

You are creating a Date using UTC time, but then you are displaying it in local time, that's why it's a few hours behind. Use Date.prototype.toUTCString() to see the UTC time
var date = new Date();
var year = date.getMonth() < 11 ? date.getFullYear() : date.getFullYear() + 1;
var month = date.getMonth() < 11 ? date.getMonth() + 1 : 0;
// It's a UTC date, display it as UTC, not local time
console.log(new Date(Date.UTC(year, month)).toUTCString());
var utcYear = date.getUTCMonth() < 11 ? date.getUTCFullYear() : date.getUTCFullYear() + 1;
var utcMonth = date.getUTCMonth() < 11 ? date.getUTCMonth() + 1 : 0;
// Created using local time, you can just use the normal toString()
console.log(new Date(utcYear, utcMonth));

This code is to get the first day of the next month (something that reoccurs monthly and can't start until next month).
Then you're looking for
var today = new Date(); // now
var utcYear = today.getUTCMonth() < 11 ? today.getUTCFullYear() : today.getUTCFullYear() + 1;
var utcMonth = today.getUTCMonth() < 11 ? today.getUTCMonth() + 1 : 0;
var date = new Date(Date.UTC(utcYear, utcMonth)); // next UTC month
console.log(date.toString()); // Mon Jun 01 2015 02:00:00 GMT+0200
// or, in your timezone: Sun May 31 2015 19:00:00 GMT-0500 (same moment)
console.log(date.toUTCString()); // Mon, 01 Jun 2015 00:00:00 GMT
Btw, the Date methods does take too large values into accout (and carry-over them automatically), so you just would need to do
var today = new Date(); // now
var date = new Date(Date.UTC(today.getUTCFullYear(), today.getUTCMonth()+1)); // next UTC month

Convert Date Format in JSON variable

I have a variable that contains JSON data with thousands of rows. Some of the variables are dates in the following format Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time). I need to convert all of these variables into a more usable date format such as `mm/dd/yyyy'.
Any suggestions on how to accomplish this?
{
"request": [
{ "startdate":"Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time)" ,
"status":"in progress" }, ...
]}
Thanks in advance!

You can pass the date string as an argument when instantiating the Date class. Javascript doesn't have a good date formatter, but you can easily roll your own. For instance:
function parseDate(date) {
var d = new Date(date);
var month = d.getMonth() + 1;
var day = d.getDate();
var year = d.getFullYear();
if(month < 10) month = '0' + month;
if(day < 10) day = '0' + day;
return month + '/' + day + '/' + year;
}
parseDate('Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time)');
// returns "06/27/2008"

Try the following:
var json = {
"request": [
{ "startdate":"Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time)" ,
"status":"in progress" }
]};
var date = new Date(json.request[0].startdate);
var formatDate = function(date) {
var mm = date.getMonth()+1;
mm = mm > 10 ? mm : "0"+mm;
var dd = date.getDate();
dd = dd > 10 ? dd : "0"+dd;
var yy = date.getFullYear();
return mm+"/"+dd+"/"+yy;
}
var formattedDate = formatDate(date);

Always best to convert a string to a date object is to manually parse it unless you have a very controlled environment. The following should do the job:
// Use date string to create a UTC time to pass to Date constructor
// Expected format is day mon year hh:mm:ss GMToffset (timezone name)
// e.g. Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time)
function parseDate(s) {
var months = {jan:0, feb:1, mar:2, apr:3, may:4, jun:5,
jul:6, aug:7, sep:8, oct:9, nov:10, dec:11};
var s = s.split(/[ :]/g);
var offset = s[7];
// Deal with offset
var sign = offset.indexOf('-') >= 0? -1 : 1;
var len = offset.length;
var offMins = sign * offset.substring(len-4, len-2) * 60 + sign * offset.substring(len-2, len);
var mins = s[4] - offMins;
return new Date(Date.UTC(s[3], months[s[1].toLowerCase()], s[2], s[4], mins, s[6]));
}
var s = 'Fri Jun 27 2008 00:00:00 GMT-0700 (US Mountain Standard Time)';
alert(parseDate(s)); //Fri 27 Jun 2008 17:00:00 GMT+1000
You can then format the date however you want:
function formatDateUS(d) {
function z(n){return (n<10? '0':'') + n}
return z(d.getMonth()+1) + '/' + z(d.getDate()) + '/' + d.getFullYear();
}
formatDateUS(parseDate(s)); // 06/27/2008