html set input type date to disable previous dates

1$(function(){
2    var dtToday = new Date();
3    
4    var month = dtToday.getMonth() + 1;
5    var day = dtToday.getDate();
6    var year = dtToday.getFullYear();
7    if(month < 10)
8        month = '0' + month.toString();
9    if(day < 10)
10        day = '0' + day.toString();
11    
12    var maxDate = year + '-' + month + '-' + day;
13    alert(maxDate);
14    $('#txtDate').attr('min', maxDate);
15});