Something

function ClearTxt() {
  document.getElementById("zipcode").value = ""
}

function validate() {

  if (/^\d{5}(?:-\d{4})?$/.test(document.getElementById("zipcode").value)) {
     alert("Please enter a valid zipcode  thanks...");
     return false;
  }

  if (document.getElementById("zipcode").value.length < 1) {
     alert("Please enter a zipcode to search EconoRooter.");
     return false;
  }

return true;

}