How do I pass JavaScript variables to PHP

Question

I want to pass JavaScript variables to PHP using a hidden input in a form.

But I can't get the value of $_POST['hidden1'] into $salarieid. Is there something wrong?

Here is the code:

<script type="text/javascript">
    // View what the user has chosen
    function func_load3(name) {
        var oForm = document.forms["myform"];
        var oSelectBox = oForm.select3;
        var iChoice = oSelectBox.selectedIndex;
        //alert("You have chosen: " + oSelectBox.options[iChoice].text);
        //document.write(oSelectBox.options[iChoice].text);
        var sa = oSelectBox.options[iChoice].text;
        document.getElementById("hidden1").value = sa;
    }
</script>

<form name="myform" action="<?php echo $_SERVER['$PHP_SELF']; ?>" method="POST">
    <input type="hidden" name="hidden1" id="hidden1" />
</form>

<?php
   $salarieid = $_POST['hidden1'];
   $query = "select * from salarie where salarieid = ".$salarieid;
   echo $query;
   $result = mysql_query($query);
?>

<table>
   Code for displaying the query result.
</table>

Niroj · Answer 1 · Jul 6, 2020

Hello @kartik,

You cannot pass variable values from the current page JavaScript code to the current page PHP code. PHP code runs at the server side, and it doesn't know anything about what is going on on the client side.

You need to pass variables to PHP code from the HTML form using another mechanism, such as submitting the form using the GET or POST methods.

<DOCTYPE html>
<html>
  <head>
    <title>My Test Form</title>
  </head>

  <body>
    <form method="POST">
      <p>Please, choose the salary id to proceed result:</p>
      <p>
        <label for="salarieids">SalarieID:</label>
        <?php
          $query = "SELECT * FROM salarie";
          $result = mysql_query($query);
          if ($result) :
        ?>
        <select id="salarieids" name="salarieid">
          <?php
            while ($row = mysql_fetch_assoc($result)) {
              echo '<option value="', $row['salaried'], '">', $row['salaried'], '</option>'; //between <option></option> tags you can output something more human-friendly (like $row['name'], if table "salaried" have one)
            }
          ?>
        </select>
        <?php endif ?>
      </p>
      <p>
        <input type="submit" value="Sumbit my choice"/>
      </p>
    </form>

    <?php if isset($_POST['salaried']) : ?>
      <?php
        $query = "SELECT * FROM salarie WHERE salarieid = " . $_POST['salarieid'];
        $result = mysql_query($query);
        if ($result) :
      ?>

Hope it helps!!

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