How to subtract one day from a date value - scoped application email script

[Nestor Padilla1]

Hello ServiceNow Experts,

I've been struggling to subtract one day from a date value I get from a custom table in a Scoped Application.

The idea behind this is that if the "end date" value I get falls on a Sunday, then in the email notification I should add some text to do something on Saturday.

For that I need to subtract one day from the end day if end day is a Sunday.

With this code I can validate if it is Sunday 

(function runMailScript( /* GlideRecord */ current, /* TemplatePrinter */ template,
    /* Optional EmailOutbound */
    email, /* Optional GlideRecord */ email_action,
    /* Optional GlideRecord */
    event) {

    var endDate = new GlideDate();
	endDate.setValue(current.planned_end);
	var dateString = endDate.getByFormat('EEEE, MMM d'); // e.g. Friday June 3
	var sunday = dateString.indexOf('Sunday');
	if (sunday > -1) {
		var saturday = endDate.addDaysLocalTime(-1);
		
	}

    if (sunday > -1) {
        template.print("<br /><p><strong><span>Since this observance includes Sunday, Operators have the option of:</strong></span></p><ul><li>Removing the American flag at sunset on " + saturday.getByFormat('EEEE, MMM d') + "</li><li>Returning the flag to full-staff at sunset on " + dateString + "</li>");
    } else {
        return;
    }

})(current, template, email, email_action, event);

I'm sure I have something wrong in my code. I was hoping someone could help me fix it.

I can't get to subtract 1 day from the end date and then format that result. Maybe my understanding of how date/time data is handled is wrong.

Thanks 

[Nestor Padilla1 · Accepted solution]

(function runMailScript(/* GlideRecord */ current, /* TemplatePrinter */ template,
		/* Optional EmailOutbound */ email, /* Optional GlideRecord */ email_action,
		/* Optional GlideRecord */ event) {
	
	var todayDate = new GlideDate().getByFormat('EEEE, MMM d');
	var endDate = new GlideDate();
	endDate.setValue(current.planned_end);
	var dateString = endDate.getByFormat('EEEE, MMM d'); // e.g. Friday June 3
	var sundayString = dateString.indexOf("Sunday");

	var getSaturday = new GlideDateTime(current.planned_end);
	getSaturday.addDaysLocalTime(-0);
	var saturday = getSaturday.getLocalDate();
	
	if (sundayString > -1) {
		
		template.print("Remove it on " + saturday.getByFormat('EEEE, MMM d') + ", and BLAH BLAH BLAH); // The output is Remove it on Saturday, Month Day ie Saturday Jun 19

		} else {
			return;
		}

})(current, template, email, email_action, event);

I ended up with the following code and works OK.

For some reason when I set getSaturday.addDaysLocalTime(-1) I get Friday. So I guess SN counts starting from 0.

I hope this helps anyone with the same issue.