I have two forms (consisting of checkboxes) on two different PHP pages. I want to use the values submitted from the first form to disable checkboxes in the second form.

page1.php:

<form method="POST" action="page2.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

page2.php:

<form method="POST" action="action.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

<script>
if(!isset($_POST['2'])){
document.getElementById("4").disabled = true;
}
</script>

What should I use instead of this?

if(!isset($_POST['2']))

I can't use jQuery due to professor limitations.

I have two forms (consisting of checkboxes) on two different PHP pages. I want to use the values submitted from the first form to disable checkboxes in the second form.

page1.php:

<form method="POST" action="page2.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

page2.php:

<form method="POST" action="action.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

<script>
if(!isset($_POST['2'])){
document.getElementById("4").disabled = true;
}
</script>

What should I use instead of this?

if(!isset($_POST['2']))

I can't use jQuery due to professor limitations.

• javascript
• php

8 Answers 8

First don't forget that you need name attributes on your checkboxes for PHP. Second, although your ids are valid in HTML5, I'd change them to start with a letter to make them HTML4 patible.

I print the POST variable using php and assign it to post in javascript. Then I check if the checkbox exists in the post variable.

page1.php:

<form method="POST" action="page2.php">
<input type="checkbox" id="1" name="box1">
<input type="checkbox" id="2" name="box2">
<input type="checkbox" id="3" name="box3">
<input type="checkbox" id="4" name="box4">
<input type="checkbox" id="5" name="box5">
<input type="checkbox" id="6" name="box6">
<input type="submit">
</form>

page2.php:

<form method="POST" action="action.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

<script>
var post = <?php echo json_encode($_POST) ?>;
if (!post.box2) document.getElementById("4").disabled = true;

</script>

Since JavaScript runs on the client and not the server, it's stateless. So, your JavaScript on page2.php has no idea about the values submitted from page1.php.

To solve this, you need to use PHP inside your JavaScript on page2.php like this:

<script>
if (<?php echo !isset($_POST['a']) ? 'true' : 'false'; ?>) {
    document.getElementById("4").disabled = true;
}
</script>

You can do this. Ugly but works:

<script>
if (<?php echo !isset($_POST['2']); ?>) {
    document.getElementById("4").disabled = true;
}
</script>

Your checkboxes must have a name:

<form method="POST" action="page2.php">
    <input type="checkbox" name="someVar1" id="someVar1" />
    <input type="checkbox" name="someVar2" id="someVar2" />
    <input type="checkbox" name="someVar3" id="someVar3" />
</form>

Then inside the script on the second page:

<script>
<?php 
if( !isset($_POST['someVar2']) || !$_POST['someVar2'] ){
    echo 'document.getElementById("someVar2").disabled = true;';
}
?>
</script>

Try this:

<?php if (!isset($_POST['2'])) { ?>
<script>
document.getElementById("4").disabled = true;
</script>
<?php } ?>

A PHP solution to your question:

<input type="checkbox" id="2" name="2" />

<!-- ... -->

<!-- rather than disable if it isn't set, only show if it is set -->
<?php if (isset($_POST['2'])) { ?>
  <input type="checkbox" id="4" name="4" />
<?php } ?>

Note that your inputs must have a name.

Can try something like below

var post_val = <?= json_encode($_POST) ?>;
if (typeof post_val['2'] == 'undefined') {
   document.getElementById("4").disabled = true;
 }

Jquery can make it simple: for input/textarea/, you can use $('#id_for_input_or_textarea').val() != '' to check whether it's empty. for radio/checkbox, you can use $(':radio:checked').length != 0 /$(':checkbox:checked').length != 0 to check whether a group of them are checked. or $('#some_radio').prop('checked') to check if a radio/checkbox is checked.