使用javascript设置input元素的值并使用php获取值

Question

Here I have a form and input element:

cart.php

<form id="cartform" action="cart.php?action=update&pd=<?php echo $row['product_id'] ?>" name="form1" method="post">
<?php
    $query = "select * from cart where customer_id='$user' ";
    $result = mysqli_query($con,$query);$payableamount = 0;$totalsavings = 0;
    while($row = mysqli_fetch_array($result))
    {
        $productid = $row['product_id'];
        $query2 = "select * from product where product_id='$productid'";
        $result2 = mysqli_query($con,$query2);
        while($row2=mysqli_fetch_array($result2))
        {
?>
            <input tpe="text"  name="quantxt[]" id="quantxt" value="<?php echo $qty = $row['quantity']; ?>" onkeyup="showsubmit(<?php echo $row['cart_id'] ?>,<?php echo $row['product_id'] ?>)">
            <input type="text" name="s1" id="s1" value=""/>
            <input style="visibility:hidden;width:80px;border-radius:10px;background-color:green;border:none;padding:5px;color:white;"
               type="submit"
               name="sub_<?php echo $row['cart_id'] ?>"
               id="sub_<?php echo $row['cart_id'] ?>"
               value="UPDATE">
</table>    
</form>

and the javascript is:

<script>
    function showsubmit(id,prodid)
    {
        alert(id);
        alert(prodid);
        document.getElementById("sub_"+id).style.visibility ="visible";
        document.getElementById("s1").value = prodid;
        f = document.getElementById("s1").value;
        alert("product id is:"+f);
    }
</script> 

when i am accessign the value of s1 element in cart2.php it gives nothing. on next page s1 has no value,while i am expecting the value that is updated using javascript

$prod_id = $_POST['s1'];
echo "product id of clickable product is:".$prod_id."<br>";

Answer 1

this line:

<input type="text" name="s1" id="s1" value=""/>

is inside a loop. can you make sure that the loop only has one row returning? because if not, then you're creating multiple elements with same id which javascript can not catch properly. id is supposed to be unique. in the case of multiple same ids it'll catch the first match and stop.