Try to add dynamic value into drop down list

Hello friends ,

I am try to add dynamic value in drop down list but get below error message 

 Please help me, my javascript code is below, code is triger on form populated event. 

var startDate=0,finishdate=0;
function pad(x) {
return (x < 10) ? "0" + x : "" + x;
}
function DateFormate(dateFormate) {
var myDate = new Date(dateFormate);
var dateString = myDate.getFullYear()+ "-";
startDate=myDate.getFullYear();
dateString += pad(myDate.getMonth() + 1) + "-";
dateString += pad(myDate.getDate());

return dateString;
}
function DateFormate1(dateFormate) {
var myDate = new Date(dateFormate);
var dateString = myDate.getFullYear()+ "-";
finishdate=myDate.getFullYear();
dateString += pad(myDate.getMonth() + 1) + "-";
dateString += pad(myDate.getDate());

return dateString;
}
var inn=new Innovator();
var Project=inn.newItem();
Project.loadAML("<Item type='project' select='id,project_number,date_start_target,date_due_target' action='get'>"+
"<project_number condition='eq'>"+document.thisItem.getProperty("project_number")+"</project_number>"+
"</Item>"
)
var projectR=Project.apply();
DateFormate(projectR.getProperty("date_start_target"));
DateFormate1(projectR.getProperty("date_due_target"));
var difBetweenstartandfin=parseFloat(finishdate)-parseFloat(startDate)

//var selectObj = document.all.from_year;

//var selectObj =getFieldByName("from_year")

I tried one line statement of code from both marked line,but get every time same error message.

var opt = document.createElement("OPTION");
//alert(opt)
selectObj.options.add(opt); // Error is coming on this point.

//selectObj.add(opt)
for(var i=0;i<=difBetweenstartandfin;i++)
{
startDate=startDate+i;
//alert(startDate)

opt.innerText = startDate;
opt.value = startDate;

}

Thank in advance ,

Ashok Kumar Yadav