title: Jquery sum and subtract based values on textbox
body: <p>1) I have <strong>3 text boxes</strong> if first text box is filled second is automatically updated from DB and added to fill third.</p>
  
  <p>2) however if 3rd text box is chosen then second is automatically updated from DB,  subtract 3rd and second to fill 1st text box. </p>
  
  <p></p>
  
  <pre><code>    &lt;td&gt;Sending Amount&lt;/td&gt;
      &lt;td&gt;&lt;input class="txt" type="text" name="txt" id = "sending"/&gt;&lt;/td&gt;
  
  
      &lt;td&gt;Charge&lt;/td&gt;
      &lt;td&gt;&lt;input class="txt" type="text" name="txt" id = "charge"/&gt;&lt;/td&gt;
  
  
      &lt;td&gt;Total Amount&lt;/td&gt;
      &lt;td&gt;&lt;input class="txt" type="text" name="txt" id = "totalAmount"/&gt;&lt;/td&gt;
  &lt;/tr&gt;
  </code></pre>
  
  <p>
   </p>
  
  <pre><code>    $(function () {
          var sending = $('input:text[id$=sending]').keyup(foo);
          var charge = $('input:text[id$=charge]').keyup(foo);            
          var totalAmount = $('input:text[id$=totalAmount]').keyup(foo);   
  
       function foo() {
  
              var value1 = sending.val();
              var value2 = charge.val();               
              var sum = add(value1, value2);
              $('input:text[id$=totalAmount]').val(sum);
      var sub = sub(value1, value2);
              $('input:text[id$=sending]').val(sub);
          }
  
          function add() {
  
              var sum = 0;
              for (var i = 0, j = arguments.length; i &lt; j; i++) {
                  if (IsNumeric(arguments[i])) {
                      sum += parseFloat(arguments[i]);
                  }
              }
              return sum;
          }
  
    function sub() 
           {
              var sub= 0;
              ***//need to create subtract function***
              }
              return sub;
          }
  
          function IsNumeric(input) {
              return (input - 0) == input &amp;&amp; input.length &gt; 0;
          }
      });
  &lt;/script&gt;
  </code></pre>
  
  <p><strong>addition is working fine subtraction is not displaying correct value.</strong> </p>
  
  <p>Tried below script, I think it does add and subtract .</p>
  
  <pre><code>  &lt;script type="text/javascript"&gt;
     $(function () {
      var sending = $('input:text[id$=sending]').keyup(foo);
      var charge = $('input:text[id$=charge]').keyup(foo);            
      var totalAmount = $('input:text[id$=totalAmount]').keyup(foo);   
   function foo() {
          var value1 = sending.val();
          var value2 = charge.val();   
  
          if(IsNumeric(value2)){
          if(IsNumeric(value1)){
          var value3 = parseFloat(value1) + parseFloat(value2);
          $('input:text[id$=totalAmount]').val(value3);
          }}
  
          value3 = totalAmount.val();
          if(IsNumeric(value3)){
          if(IsNumeric(value2)){
          value1 = parseFloat(value3) - parseFloat(value2);
          $('input:text[id$=sending]').val(value1);
          }}
      }
      function IsNumeric(input) {
          return (input - 0) == input &amp;&amp; input.length &gt; 0;
      }
  });
  </code></pre>
  
  <p></p>