如果提交表单，则显示错误

Question

I'm wanting my form to show an error such as "Enter first name" if the field has not being filled in. I have got to right code(I think) to do this but it is showing the error when the page is first loaded. I want it to be displayed when the form has been submitted.

    <div class="Row">
<div class="Lable">First Name:</div> <!--End of Lable-->
<div class="input">
<input type="text" id="firstname" class="detail" name="firstname" placeholder="First Name"  />
</div> <!--End input-->
</div> <!--End row-->
<span class="error">* <?php echo $nameErr;?></span>

The PHP validation is

 if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["firstname"])) {
 $nameErr = "Name is required";
} else {
 $firstname = test_input($_POST["name"]);
 // check if name only contains letters and whitespace
 if (!preg_match("/^[a-zA-Z ]*$/",$firstname)) {
   $nameErr = "Only letters and white space allowed"; 
 }
}

Thanks

Answer 1

I would double check the form with PHP and JavaScript

For the javascript part add this line to your form, so the function validate() will run before the forms content will be sent to the server.

<form onsubmit="validate()">

Then you can add a javascipt function to your document like this:

function validate() {
  if (/*check if fields are filled out properly*/) {
    this.submit();
  } else {
    // show message here when fields are missing

    return false; // this line is important otherwise the form gets submitted anyway
  }
}

For the PHP part it is enough to check for the differnt fields with isset()

This would look like this:

$formOK = true;
if (!isset($_POST["field-name-1"]) || $_POST["field-name-1"] == "") {
  echo "field-1 is missing";
  $formOK = false
}
if (!isset($_POST["field-name-2"]) || $_POST["field-name-2"] == "") {
  echo "field-2 is missing";
  $formOK = false
}

if (formOK) {
  echo "everything is fine";
  // do something with your form data
}

---

To double check is definitly the best way because first of all you are not having so many requests and the javascript is more flexible in is reactions and speed but the PHP will provide you the guarantee that nothing will go wrong.