var currentTime = new Date();
var year = currentTime.getFullYear();
var yearminus1 = year-1;
var yearplussone = year+1;
var yearplusstwo = year+2;

document.write('<option>'+yearminus1+'</option>');
document.write('<option>'+year+'</option>');
document.write('<option>'+yearplussone+'</option>');
document.write('<option>'+yearplusstwo+'</option>');