Why does my code fail to retain checkbox selection?

Other Questions JavaScript
1

I’m scratching my head over a weird issue in my web app. It uses PHP, JavaScript, and HTML to display form data from a SQLite database. The problem shows up when I call either form_function_1 or form_function_2.

Here’s what happens:

  1. I check a box in the form
  2. It triggers an auto-submit
  3. The checkbox unchecks itself right away
  4. The submit button gets disabled
  5. I can’t type anything in the form

I’ve tried switching the order of function calls, but it’s always the first one that acts up. I think it might be a JavaScript problem, but I’m not sure.

Here’s a simplified version of my code:

function getData($tableName) {
  $db = new PDO('sqlite:mydb.sqlite');
  $query = $db->query("SELECT * FROM $tableName ORDER BY id DESC LIMIT 1");
  return $query->fetch(PDO::FETCH_ASSOC);
}

function renderForm($id, $sensorData) {
  $value = $_GET["value$id"] ?? $sensorData['value'];
  $checked = isset($_GET["checkbox$id"]) ? 'checked' : '';
  
  echo "<form id='form$id' method='GET'>
    {$sensorData['name']} ({$sensorData['unit']})
    <input type='text' name='value$id' value='$value' $checked>
    <input type='checkbox' id='check$id' name='checkbox$id' $checked>
    <input type='submit' value='Send' $checked>
  </form>

  <script>
    document.querySelector('#check$id').onchange = function() {
      this.form.submit();
    };
  </script>";
}

$pressure = getData('Pressure');
$temp = getData('Temperature');

renderForm(1, $pressure);
renderForm(2, $temp);

Any ideas on what’s causing this behavior?

2

I encountered a similar situation when my forms wouldn’t retain their state. In my experience the issue usually arises because the browser reloads the page upon submission. A good first step is to call event.preventDefault() in your JavaScript so that the form does not trigger a full page refresh. Using AJAX for form submission instead of a traditional post can also help preserve state. Another trick is to include a hidden input so that a default value is sent even if the checkbox is unchecked. Adjusting your PHP to handle this input properly should resolve the problem.

3

I’ve seen this issue before in my own projects. It’s likely due to the form submitting and reloading the page, which resets all form elements. To fix this, you need to prevent the default form submission behavior.

Try modifying your JavaScript to use preventDefault():

document.querySelector('#check$id').onchange = function(event) {
  event.preventDefault();
  // Add your submission logic here
  // You can use AJAX to submit the form data without page reload
};

This will stop the page from reloading when the checkbox is clicked. You’ll then need to implement your own logic to handle the form submission, possibly using AJAX to send the data to the server without a full page refresh.

Also, consider adding a hidden input to track the checkbox state:

<input type='hidden' name='checkbox$id' value='0'>
<input type='checkbox' id='check$id' name='checkbox$id' value='1' $checked>

This ensures the checkbox state is always sent, even when unchecked.

4

hey, i’ve run into this before. the problem’s probably cuz the page reloads when u submit the form. try using event.preventDefault() in ur javascript to stop that:

document.querySelector(‘#check$id’).onchange = function(event) {
event.preventDefault();
// do ur form stuff here without reloading
};

also, maybe add a hidden input to keep track of the checkbox:

hope this helps!