Start Date and End Date in Bootstrap

if user clicks on fromDate first set enddate for toDate and if user clicks on toDate first we have to set start date for fromDate.

we have to also provide date format if needed.

$(document).ready(function(){
   $("#fromDate").datepicker({
       format: 'dd-mm-yyyy',
       autoclose: true,
   }).on('changeDate', function (selected) {
       var minDate = new Date(selected.date.valueOf());
       $('#toDate').datepicker('setStartDate', minDate);
   });

   $("#toDate").datepicker({
       format: 'dd-mm-yyyy',
       autoclose: true,
   }).on('changeDate', function (selected) {
           var minDate = new Date(selected.date.valueOf());
           $('#fromDate').datepicker('setEndDate', minDate);
   });
});

<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" rel="stylesheet"/>
<link href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.9.0/css/bootstrap-datepicker.min.css" rel="stylesheet"/>
<form autocomplete="off">
<input type="text" id="fromDate">
<input type="text" id="toDate">
</form>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.9.0/js/bootstrap-datepicker.min.js"></script>

At the time you set $('#toDate').datepicker() , the value of $('#fromDate') is empty.

You should set default startDate and endDate variables at the begining and add changeDate event listener to your datepickers.

Eg.:

// set default dates
var start = new Date();
// set end date to max one year period:
var end = new Date(new Date().setYear(start.getFullYear()+1));

$('#fromDate').datepicker({
    startDate : start,
    endDate   : end
// update "toDate" defaults whenever "fromDate" changes
}).on('changeDate', function(){
    // set the "toDate" start to not be later than "fromDate" ends:
    $('#toDate').datepicker('setStartDate', new Date($(this).val()));
}); 

$('#toDate').datepicker({
    startDate : start,
    endDate   : end
// update "fromDate" defaults whenever "toDate" changes
}).on('changeDate', function(){
    // set the "fromDate" end to not be later than "toDate" starts:
    $('#fromDate').datepicker('setEndDate', new Date($(this).val()));
});