title: Try and catch for check sum validation on input to check three parts of an input in Javascript
body: <p>Bouncing my head off the wall here trying to figure out a better way to handle this. I have a large input value which has three checks to check the sum of certain parts of the string in order to validate it. I'm using three try/catch blocks in one function to run the check right now and it seems to be working except for the final validation check which always seems to return true. What I'm wondering is a) is this a good method to use, b) is there a cleaner way to do this with for loop and c) why my final check is not doing anything. Any help is appreciated. I have access to jQuery and Underscore.js if that helps but I have not worked much with underscore. I made a fiddle here:</p>
  
  <p><a href="http://jsfiddle.net/nkb5sbhv/6/" rel="nofollow">Sample Fiddle</a></p>
  
  <pre><code>     window.onkeyup = keyup;
      var number;
  
      function keyup(e) {
          number = e.target.value;
          $('#numberValue').text(number);
          // must be 10 characters long
          if (number.length !== 30) {
              return false;
          }
          number = "" + (number || "");
          // run the checksum
          var valid = false;
          try {
              var sum = (parseInt(number[0]) * 7) +
                      (parseInt(number[1]) * 3) +
                      (parseInt(number[2])) +
                      (parseInt(number[3]) * 7) +
                      (parseInt(number[4]) * 3) +
                      (parseInt(number[5])) +
                      (parseInt(number[6]) * 7) +
                      (parseInt(number[7]) * 3) +
                      (parseInt(number[8]));
              alert(((sum % 10).toFixed(0)));
              var checkDigit = ((sum % 10).toFixed(0));
  
              if ((number[9]) === ("" + checkDigit)) {
                  alert('Our Checkdigit is valid', checkDigit);
                  valid = true;
              }
          } catch (e) {
              alert('Fail for check 1!');
              valid = false;
          }
          try {
              var sum2 = (parseInt(number[13]) * 7) +
                      (parseInt(number[14]) * 3) +
                      (parseInt(number[15])) +
                      (parseInt(number[16]) * 7) +
                      (parseInt(number[17]) * 3) +
                      (parseInt(number[18]));
              alert(((sum2 % 10).toFixed(0)));
              var checkDigit2 = ((sum2 % 10).toFixed(0));
  
              if ((number[19]) === ("" + checkDigit2)) {
                  alert('Our Checkdigit2 is valid', checkDigit2);
                  valid = true;
              }
          } catch (e) {
              alert('Fail for check 2!');
              valid = false;
          }
          try {
              var sum3 = (parseInt(number[21]) * 7) +
                      (parseInt(number[22]) *3) +
                      (parseInt(number[23])) +
                      (parseInt(number[24]) * 7) +
                      (parseInt(number[25]) * 3) +
                      (parseInt(number[26]));
              alert(((sum3 % 10).toFixed(0)));
              var checkDigit3 = ((sum3 % 10).toFixed(0));
  
              if ((number[27]) === ("" + checkDigit3)) {
                  alert('Our Checkdigit3 is valid',checkDigit3);
                  valid = true;
              }
          } catch (e) {
              valid = false;
          }
  
          alert('All Good DUde!');
          return valid;
      }
  </code></pre>