Date does not work properly

Hi,
the problem is that when the link is generated ,
it creates a day after the date that was entered.
like this:

dates=20200610/20200611

it works fine when the day in the date is 10 and up.
but it does not work with 1-9

the second date is written in one digit instead of 2
like this:

dates=20200608/2020069
and than it does not recognize the date

It is something to fix in the js:

var oneMoreDay = function( date ){
date = new Date ( date );
date.setDate( date.getDate() + 1 );
return formatDate( date );
};

//just numbers
date1 = date1.replace(/\D/g,”);

if( date2 != 0 ){
date2 = date2.replace(/\D/g,”);
} else{
date2 = oneMoreDay( date1 );
date2 = date2.replace(/\D/g,”);
}

dates = ‘dates=’ + date1 + ‘/’ + date2;

How can taht be solved?

Thanks
Michal