JavaScript date : How to compare two dates to check which one is greater?

Example:

if(startDate.getTime() == endDate.getTime()) //both the dates are same
{
            //do something
}

JavaScript date : How to get days between two dates?

var daysInbetween = (d2.getTime() - d1.getTime())/(1000 * 3600 * 24);

JavaScript date : How to get all dates between two dates?

function getAllDatesBetween(startDate,endDate)
{
var d1 = new Date(startDate);
var d2 = new Date(endDate);
var d3;
var daysInbetween = (d2.getTime() - d1.getTime())/(1000 * 3600 * 24);

for(var i=0;i<=daysInbetween;i++)
{
d3 = new Date(d1);
d3.setDate(d3.getDate() + i);
datesArray.push((d3.getMonth()+1).toString()+"/"+d3.getDate().toString()+"/"+d3.getFullYear().toString());
}
}

JavaScript date : How to get date for first, mid and last day of a month?

var firstDayStartDate = new Date(anyDateOfTheMonth.getFullYear(), anyDateOfTheMonth.getMonth(), 1);

var midDayStartDate = new Date(anyDateOfTheMonth.getFullYear(), anyDateOfTheMonth.getMonth(), 15);

var midDayPlusOneStartDate = new Date(anyDateOfTheMonth.getFullYear(), anyDateOfTheMonth.getMonth(), 16);

var lastDayStartDate = new Date(anyDateOfTheMonth.getFullYear(), anyDateOfTheMonth.getMonth() + 1, 0);

JavaScript Date : How to get working hours between two dates?

function getWorkingHoursBetween(d1,d2)
{
var workingDays = 0;
var daysInbetween = (d2.getTime() - d1.getTime())/(1000 * 3600 * 24);
var d3, iDay;
for(var i=0;i<=daysInbetween;i++)
{
d3 = new Date(d1);
d3.setDate(d3.getDate() + i);
iDay = d3.getDay();
if(iDay !=0 && iDay!=6)
{
workingDays++;
}
}
return (workingDays*9); //9 being the working hours per day
}

SPQuery: How to fetch SharePoint list data for a particular date?

startDate = "2019-8-27";
endDate = "2019-8-27":

"<Query>"+
  "<Where>"+
    "<And>"+
        "<Leq><FieldRef Name='Some_x0020_DATE'/><Value Type='DateTime'>"+endDate+"T23:59:00.000Z</Value></Leq>"+
        "<Geq><FieldRef Name='Some_x0020_DATE'/><Value Type='DateTime'>"+startDate +"T00:00:00.000Z</Value></Geq>"+
     "</And>"+
  "</Where>"+
"</Query>";

SPQuery: How to filter based on modified date?

<Query>
    <Where>
        <Leq>
            <FieldRef Name="DateColumn" />
            <Value Type="DateTime">
                <Today OffsetDays="-4" /> // Modified in last 4 days
            </Value>
        </Leq> 
    </Where>
</Query> 

InfoPath: How apply formatting rule of a date field?

Add the 'Date' field to the form, and change the control to 'Text Box'

SPServices : How to prepare date data for the SharePoint list date field using JavaScript?

var currDate = new Date();

var numDay=currDate.getDate();
var numMonth = currDate.getMonth();
var numYear = currDate.getFullYear();

var tempDate = (++numMonth)+"/"+(numDay)+"/"+numYear ;
var spDate = new Date(tempDate).toISOString();

//e.g. 2019-08-29T18:30:00.000Z


Note: You may have to adjust numDay based on the timezone.

How to find the day number from today's date in SharePoint designer 2013?