How to I Send Data from JavaScript to PHP and Vice Versa

How to pass data from Javascript to PHP and vice versa?

Passing data from PHP is easy, you can generate JavaScript with it. The other way is a bit harder - you have to invoke the PHP script by a Javascript request.

An example (using traditional event registration model for simplicity):

<!-- headers etc. omitted -->
<script>
function callPHP(params) {
    var httpc = new XMLHttpRequest(); // simplified for clarity
    var url = "get_data.php";
    httpc.open("POST", url, true); // sending as POST

    httpc.onreadystatechange = function() { //Call a function when the state changes.
        if(httpc.readyState == 4 && httpc.status == 200) { // complete and no errors
            alert(httpc.responseText); // some processing here, or whatever you want to do with the response
        }
    };
    httpc.send(params);
}
</script>
<a href="#" onclick="callPHP('lorem=ipsum&foo=bar')">call PHP script</a>
<!-- rest of document omitted -->

Whatever get_data.php produces, that will appear in httpc.responseText. Error handling, event registration and cross-browser XMLHttpRequest compatibility are left as simple exercises to the reader ;)

See also Mozilla's documentation for further examples

How to I send data from JavaScript to PHP and vice versa?

If you wish to submit this data via a form, you don't need to create the form with Javascript. Simply create an invisible form with HTML, populate the hidden field with Javascript, and automatically submit whenever you're ready.

  <form method="post" action="process.php">
    <input type="hidden" name="data" id="data" />
  </form>

  document.getElementById("data").value = "foo";

If you want to send this in an ajax-style fashion, I would suggest implementing jQuery, which makes this extremely easy. Note the previous case converted to a jQuery solution:

$.post("process.php", {data:"foo"}, function(results){
  // the output of the response is now handled via a variable call 'results'
  alert(results);
});

How do I pass JavaScript variables to PHP?

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 ($result) :
      ?>
        <table>
          <?php
            while ($row = mysql_fetch_assoc($result)) {
              echo '<tr>';
              echo '<td>', $row['salaried'], '</td><td>', $row['bla-bla-bla'], '</td>' ...; // and others
              echo '</tr>';
            }
          ?>
        </table>
      <?php endif?>
    <?php endif ?>
  </body>
</html>

how to send data from js to php and vice versa?

I think @Moob is right.

Why don't you try something like :

var obj = {};
obj.name_of_parameter = val
// val is your param ...
// and name_of_parameter as to match your php get or post variable name

var str = jQuery.param(obj);

$.ajax({
    type: "POST",
    url: 'the_url',
    dataType: 'json',
    data: str,
    success: function (data) {
            // code if ok
    },

    error: function() {
        // code if something went wrong
    }
});

passing PHP variable in Javascript and vice versa

You need to quote the string in the onclick:

echo "<td><a href='#' onclick='disp_confirm(\"{$row->university}\")'>Delete</a></td>";

Pass javascript variable to php code?

You can't directly do that, since JavaScript runs on the client-side and PHP gets executed on the server-side.

You would need to execute the JavaScript first and then send the result to the server via a FORM or AJAX call.

Here's what that might look like:

PHP

$parameter = "this is a php variable";
echo "var myval = foo(" . parameter . ");";

JavaScript

var myval = foo("this is a php variable"); // generated by PHP

$.ajax({
  type: 'POST',
  url: 'yourphpfile.php',
  data: {'variable': myval},
});

Receiving PHP (yourphpfile.php)

$myval = $_POST['variable'];
// do something

How to assign the javascript variable value to php variable

Javascript works on the user's computer, PHP works on your server. In order to send variables from JS to PHP and vice versa, you need communication such as a page load.

Have a look here on what you can do: How to pass JavaScript variables to PHP? or more specifically the first answer (https://stackoverflow.com/a/1917626/1311593)