How to return the key of an array element?

Question

PHP

There is an array $_POST.
How to get element key from this array?
for example, there is an element $_POST['name']
How to display the key "name" without resorting to foreach ?
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$_POST comes from the user via a form. After validating the data on the server, I need to get the keys of those elements (key == id of the field in the form) that did not pass the validation and send them back (ajax) in order to match these keys with the form elements that did not pass the validation and apply certain actions to these fields .

Answer 1

Also here - php.net/manual/ru/function.key.php

Answer 2

An array key has no key in this array. He is the key.
You do something like this:

if (false === Validator::isValidName($_POST['name'])){
  $errors['name'] = 'Введите человеческое имя!';
}

<label>
  <input type="name" name="name" value="" />
  <span class="error"><?= $errors['name'] ?></span>
</label>