title: 'undefined' appearing in alert
body: <p>I am using Javascript to validate some code, and it works fine, but whenever I call alert to show the errors, at the beginning of the alert message I get 'undefined'.  So when I should expect the alert to show 'Please enter a Low Target', instead I get 'undefinedPlease enter a Low Target'.  Can somebody tell me what is wrong with my code?</p>
  
  <pre><code>//validation
          var lowTarget;
          var highTarget;
          var errorList;
          var isValid = true;
  
          lowTarget = $('input[name="txtLowTarget"]').val();
          highTarget = $('input[name="txtHighTarget"]').val();
  
          if (lowTarget == "") {
              errorList += "Please enter a Low Target\n";
              isValid = false;
          }
          else {
              if (isNumeric(lowTarget) == false) {
                  errorList += "Low Target must be numeric\n";
                  isValid = false;
              }
          }
  
          if (highTarget == "") {
              errorList += "Please enter a High Target\n";
              isValid = false;
          }
          else {
              if (isNumeric(highTarget) == false) {
                  errorList += "High Target must be numeric\n";
                  isValid = false;
              }
          }
  
          if (isValid == true) {
              if (!(parseFloat(highTarget) &gt; parseFloat(lowTarget))) {
                  errorList += "High Target must be higher than Low Target\n";
                  isValid = false;
              }
          }
  
          if (isValid == false) {
              alert(errorList);
          }
  </code></pre>