Javascript date processing time zone issue_time and date

//dateObj is a date object, days represents how much to add to this date Days, for example 4, 5 (days)
function dateAdd(dateObj,days){
var tempDate = dateObj.valueOf();
tempDate = tempDate days * 24 * 60 * 60 * 1000;
tempDate = new Date(tempDate);
return tempDate;
}

//Then use, create a date object
var dateValue = document.getElementById("XXYY"). value.split("-");
var custArvDateTwoValue = new Date(dateValue[0],dateValue[1]-1,dateValue[2]);
//Call dateAdd and add two days
custArvDateTwoValue = dateAdd(custArvDateTwoValue,2);
var year = custArvDateTwoValue.getFullYear();
var month = custArvDateTwoValue.getMonth() 1;
var days = custArvDateTwoValue.getDate();
month = month <= 9 ? "0" month : month;
days = days <= 9 ? "0" days : days;
document.getElementById("XX").value = year "-" month "-" days;