php - Is there any way that the first character of a text box is either '+' or '-' by default -

i have text field on form gmt time. want users enter integers '+5' '+6' or '-6' or '-5' etc.

i want make easy users don't have write '+' or '-' there self. there should default option of '+' or '-' first character in text field.

i saw solutions making simple drop down in front , user can select there automatically appear in text box.

but want make more easy if other easy solution there.

will prefer using html5 if not jquery fine..

try one:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script> <script>     $(document).ready(function() {          var num = 0;          $('#txt1').keydown(function(e){               num += 1;             if (e.keycode > 36 && e.keycode < 41)  {                  if(num % 2){                  $('#txt1').val('+');                  }else{                    $('#txt1').val('-');                 }                  }              });               }); </script>  <input type="text" name="txt1" id="txt1" />