firstChild这个属性是不是废除了？该如何解决

function checkDate() {
if (!document.getElementById || !document.createTextNode) {
  return;
}
var dateField = document.getElementById("date");
if (!dateField) {
  return;
}
var errorContainer = dateField.parentNode.getElementsByTagName("span")[0];
if (!errorContainer) {
  return; 
}
var checkPattern = new RegExp("\\d{2}/\\d{2}/\\d{4}");
var errorMessage = "";
errorContainer.innerHTML = '';
var dateValue = dateField.value; 
if (dateValue == "") {
  errorMessage = "Plaese provide a date.";
}
else if (!checkPattern.test(dateValue)) {
  errorMessage = "Pleaes provid the date in the defined format";
}
if (errorMessage != "") {
  errorContainer.innerHTML = errorMessage; 
  dateField.focus();
  return false;
} else {
  return true;
}
}