Question

I have a form with multiple items and an id attributed to each of these items, on Submit I want to be able to grab the id of the item that was clicked – I have tried using js, something like:

<form method="post" action="add_item_cart.php">
    <input type="hidden" id="item_id" name="item_id">
    <input name="submit_item" id="btn_sub" onclick="document.getElementById('item_id').value = <?php echo '3'; ?>" type="submit" value="Add">
</form>

I want to be able to grab this value: $item_id = $_POST["item_id"]; on add_item_cart.php, but this doesn’t seem to be working.

Is this a problem with my js syntax or is my logic not plausible to solve this problem? Is it submitting before changing the value?

EDIT:
Let’s see if I can explain myself better, I want to assign that hidden value dynamically, imagine that my form has 3 submit buttons (one for each item displayed). Depending on the one that is clicked, I want to pass the item’s id to my hidden field, so if I click button1 – $_POST[“item_id”]=1, button2 – $_POST[“item_id”]=2… etc

Here is my actual form (non simplified example)

<form method="post" action="add_item_cart.php">
                <table style="width:600px">
                    <tr>
                        <?php foreach ($items as $item): ?>
                            <td>
                        <center>
                            <span style="font-size:20px"><?php echo $item["item_name"] ?></span><br/>
                            €<?php echo $item["price"] ?><br/>
                            Quantidade: <input type="text" value="1" style="width:30px"><br/>
                            <input type="hidden" id="item_id" name="item_id">
                            <input name="submit_item" id="btn_sub" onclick="document.getElementById('item_id').value = <?php echo $item["id"]; ?>" type="submit" value="Adicionar">
                        </center>
                        </td>
                    <?php endforeach; ?>
                    </tr>
                </table> 
            </form>

Answer 1

When your form is posted and you want to collect the item_id value on add_item_cart.php first you need to actually assign a value to id as in (Assuming item_id is a php variable). The id is just used for setting the css editing not a value…

<input type="hidden" id="item_id" value="<?php echo $item_id; ?>" name="item_id">

you cannot have id=” for the value because ‘value’ is value.

Then you can get that value on your other page with:

<?php
if(isset($_POST['item_id'])){
$item_id = $_POST['item_id'];
}
?>

If you want to edit the variable after post depending on which button you hit you can try.

<input name="submit_item1" id="btn_sub" name="button1" type="submit" value="Add">
<input name="submit_item2" id="btn_sub" name="button1" type="submit" value="Add">
<input name="submit_item3" id="btn_sub" name="button1" type="submit" value="Add">

Then on the top of your page you can do.

<?php
if(isset($_POST['submit_item1'])){
$item_id = 1;
}
if(isset($_POST['submit_item2'])){
$item_id = 2;
}
if(isset($_POST['submit_item3'])){
$item_id = 3;
}
?>

If you are creating forms from an array of items you could do something like, (assuming you somehow have an id associated with those items; I would need to know more information about how you are making your item list. But it would generally do like this.

<?php
foreach($item_array as $item){
?>
<form method="post" action="add_item_cart.php">
    <input type="hidden" id="item_id" name="item_id" value="<?php echo $item['id']; ?>">
    <input name="submit_item" id="btn_sub" type="submit" value="Add">
</form>

<?php
}
?>

Then on the top of your page you can just get $_POST[‘item_id’] and since that value is dynamically set you do not need any conditionals you can just get that value and run any query.