Validate date in JavaScript (dd/mm/yyyy format)

Validatedate.js

 function validatedate() {
                  var dateText = document.getElementById("DATE_FIELD_NAME");
                  if (dateText) {
                      try {
                          var errorMessage = "";                         
                          var splitComponents = dateText.value.split('/');
                          if (splitComponents.length > 0) {
                              var day = parseInt(splitComponents[0]);
                              var month = parseInt(splitComponents[1]);
                              var year = parseInt(splitComponents[2]);

                              if (isNaN(day) || isNaN(month) || isNaN(year)) {
                                  errorMessage = "The day, month and year need to be numbers";
                                  alert(errorMessage);
                                  return false;
                              }

                              if (day <= 0 || month <= 0 || year <= 0) {
                                  errorMessage = "The day, month and year need to be positive values greater than 0";
                              }

                              if (month > 12) {
                                  errorMessage = "The month cannot be greater than 12.";
                              }

                              if (errorMessage == "") {
                                  // assuming no leap year by default
                                  var daysPerMonth = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
                                  if (year % 4 == 0) {
                                      // current year is a leap year
                                      daysPerMonth[1] = 29;
                                  }

                                  if (day > daysPerMonth[month - 1]) {
                                      errorMessage = "Number of days are more than those allowed for the month";
                                  }
                              }
                          } else {
                              errorMessage = "Please enter the date in dd/mm/yyyy format";
                          }

                          if (errorMessage) {
                              alert(errorMessage);
                              return false;
                          }
                      } catch (e) {
                          alert(e);
                          return false;
                      }
                  }

                  return true;
              }