Question

My problem is fairly simple to explain yet a little tricky to implement. Logically it seems very possible but im a little stuck.

Objective/purpose:
I have my first SELECT named “hour” and a second SELECT named “rec_hour”. Each have the same values. See HTML code below:

<select id="hour">
  <option value="0">00</option>
  <option value="1">01</option>
  <option value="2">02</option>
  <!-- This would go up to 23 -->
</select>

<select id="rec_hour">
   <option value="0">00</option>
   <option value="1">01</option>
   <option value="2">02</option>
 <!-- This would go up to 23 -->
</select>

I receive a variable from a PHP file “$hours” which contains a integer value ranging from 0 to 24. Now, I want to get that value of hours, lets say its 6 for this scenerio, and subtract this value in the second SELECT (rec_hour).

So in essence, if my returned variable is 6. and i choose say 10 from the first select (hour) then i want the second select to show/select the value that is 10-6 which is 4.

I hope that makes sense..

I have tried the script below out of desperation but to no avail:

    $(document).ready(function() {

    $("#hour").change(function() {
        var myHour = $(this).val();
        var Subtra = 10;
        var recHour = myHour - Subtra;

       $("#rec_hour").val = recHour;
       $("#rec_hour").text(recHour); 
     }
  });

});

My code above im using “Subtra” as a litmus test value.. this would actually change based on my php result.

UPDATE:

All i really want to do is this..

I receive a time (hours only) say 2 -> refers to 2am (14 would be 2pm) n then my php will calculate hours to find out how long a journy will take. For instance say tht is 6 hours.. then i want to show the user 6 hours behind from 2am..which is 8pm.. i.e. you should leave home at 8pm.. you follow? or am i confusing?

Answer 1

Set the value of rec_hour using .val(). Also note there was a few syntax errors in your code. You had an extra curly brace. Also you want to handle the case where subtra > myHour, using the abs value function.

Corrected Code:

$(document).ready(function() {

    $("#hour").change(function() {
        var myHour = $(this).val();
        var Subtra = 4;
        var recHour = Math.abs(Subtra - myHour);
       $("#rec_hour").val(recHour);
     });
});

Original With Errors Noted:

    $(document).ready(function() {

    $("#hour").change(function() {
        var myHour = $(this).val();
        var Subtra = 10;
        var recHour = myHour - Subtra;  //handle Subtra > myHour with abs()

       $("#rec_hour").val = recHour;
       $("#rec_hour").text(recHour); 
     } //This curly brace is not needed
  });

});

Demo: http://jsfiddle.net/FdW4w/3/

I gave some more descriptive variables names and applied the math. The fiddle is also updated to reflect this.

  $(document).ready(function() {

    $("#arrival").change(function() {
        var arrivalTime = $(this).val();
       $("#depart").val(getDepartTime(10, arrivalTime));
     });
});

      function getDepartTime(journeyDuration, arrivalTime){
          var departTime = 0;
          if(journeyDuration > arrivalTime){
             departTime = 24 - (Math.abs(journeyDuration - arrivalTime));             
          }else{
             departTime = arrivalTime -journeyDuration;
          }
          return departTime;
      }