Question

I have a time string populated in select/list control e.g 05:40 I want to add 20 minutes in it and populate in textbox everytime when list value get changes in jquery or javascript

$(document).ready(function() {

$("#starttimeList").change(function() {
var selectVal = $('#starttimeList').val();
    ////// HERE I WANT MY CODE AS selectVal is getting value of select control e.g. 05:40 and entTime is my textbox where I want the time added with 20 minutes.
$("#endTime").val(selectVal);

 });
});

Answer 1

If time is in the format hh:mm, you can use a simple function to convert it to minutes, add more minutes, then convert it back to hh:mm again:

function addMinutes(time/*"hh:mm"*/, minsToAdd/*"N"*/) {
  function z(n){
    return (n<10? '0':'') + n;
  }
  var bits = time.split(':');
  var mins = bits[0]*60 + (+bits[1]) + (+minsToAdd);

  return z(mins%(24*60)/60 | 0) + ':' + z(mins%60);  
}  

addMinutes('05:40', '20');  // '06:00'
addMinutes('23:50', 20);    // '00:10'
addMinutes('00:00', '120'); // '02:00'

The minutes to add can be a number or string.

If you need to allow for daylight saving, using a date object may make life easier.