Calculate end date from start date and number days to add

I'm trying to calculate a end date from a start date and number of days to add, both collected via user input. I've read the tutorials relevant and thought I understood how it worked but I can not figure out why my code wont output.

So user enters that the start date is 01/02/03 and it takes 5 days. I need the end date to output 01/07/03. I can't seem to see why it won't.

Here's what I've got:

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var startDate = this.getField("startDate_1").value; // get start date string

var endDate = this.getField("endDate_1"); // define the field the end date will be in

if(startDate.value != ""){

    var dateConverted = util.scand("mm/dd/yy", startDate); // convert string to date object

    var addDays = this.getField("days_1");

    var oneDay = 24 * 60 * 60 * 1000;

    var addDayMillis = addDays * oneDay;

    var endMillis = dateStart.getTime() + addDayMillis;

    var calcEndDate = new Date(endMillis);

    endDate.value = util.printd("mm d, yy",calcEndDate);

}

else{

    endDate.value = "----";

}

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What did I miss here?