javascript无所事事

Question

i am trying to make a finish time in a line of text update depending on the length of time selected in the drop down box relative to the start time.

so if the start time was 13:00 and the user selects 1 hour the finish time would update to 14:00

I dont have a clue what i am doing right or wrong since i dont know the first thing about javascript.

  <script type='text/javascript'>
         function changeText(){
            var option=document.getElementById('time').value;
               if(option=='30'){
                     document.getElementById('field').value='".date(strtotime("$finishtime + 30 minutes"))."';
                               }

              else if(option=='60'){
                     document.getElementById('field').value='".date(strtotime("$finishtime + 60 minutes"))."';
                               }
             }
  </script>

i dont seem to be getting any errors in the debugger and the script does nothing.

<a>Booking For ".$start." - </a><a id='field'>".$finishtime."</a><a> on ".$date."</a>

         <form enctype='multipart/form-data' method='post'>
                 <a class='1'>Session Length</a>
                       <select name='time' id='time' onchange='changeText();'>
                             <option selected='selected'></option>
                             <option id='30' value='30'>30 mins</option>
                             <option id='60' value='60'>1 Hour</option>
                       </select>

Answer 1

use

document.getElementById('field').text

instead of

 document.getElementById('field').value