Data Transfer from JavaScript to PHP

How do I pass variables and data from PHP to JavaScript?

There are actually several approaches to do this. Some require more overhead than others, and some are considered better than others.

In no particular order:

1. Use AJAX to get the data you need from the server.
2. Echo the data into the page somewhere, and use JavaScript to get the information from the DOM.
3. Echo the data directly to JavaScript.

In this post, we'll examine each of the above methods, and see the pros and cons of each, as well as how to implement them.

1. Use AJAX to get the data you need from the server

This method is considered the best, because your server side and client side scripts are completely separate.

Pros

• Better separation between layers - If tomorrow you stop using PHP, and want to move to a servlet, a REST API, or some other service, you don't have to change much of the JavaScript code.
• More readable - JavaScript is JavaScript, PHP is PHP. Without mixing the two, you get more readable code on both languages.
• Allows for asynchronous data transfer - Getting the information from PHP might be time/resources expensive. Sometimes you just don't want to wait for the information, load the page, and have the information reach whenever.
• Data is not directly found on the markup - This means that your markup is kept clean of any additional data, and only JavaScript sees it.

Cons

• Latency - AJAX creates an HTTP request, and HTTP requests are carried over network and have network latencies.
• State - Data fetched via a separate HTTP request won't include any information from the HTTP request that fetched the HTML document. You may need this information (e.g., if the HTML document is generated in response to a form submission) and, if you do, will have to transfer it across somehow. If you have ruled out embedding the data in the page (which you have if you are using this technique) then that limits you to cookies/sessions which may be subject to race conditions.

Implementation Example

With AJAX, you need two pages, one is where PHP generates the output, and the second is where JavaScript gets that output:

get-data.php

/* Do some operation here, like talk to the database, the file-session
 * The world beyond, limbo, the city of shimmers, and Canada.
 *
 * AJAX generally uses strings, but you can output JSON, HTML and XML as well.
 * It all depends on the Content-type header that you send with your AJAX
 * request. */

echo json_encode(42); // In the end, you need to `echo` the result.
                      // All data should be `json_encode`-d.

                      // You can `json_encode` any value in PHP, arrays, strings,
                      // even objects.

index.php (or whatever the actual page is named like)

<!-- snip -->
<script>
    fetch("get-data.php")
        .then((response) => {
            if(!response.ok){ // Before parsing (i.e. decoding) the JSON data,
                              // check for any errors.
                // In case of an error, throw.
                throw new Error("Something went wrong!");
            }

            return response.json(); // Parse the JSON data.
        })
        .then((data) => {
             // This is where you handle what to do with the response.
             alert(data); // Will alert: 42
        })
        .catch((error) => {
             // This is where you handle errors.
        });
</script>
<!-- snip -->

The above combination of the two files will alert 42 when the file finishes loading.

Some more reading material

• Using the Fetch API
• How do I return the response from an asynchronous call?

2. Echo the data into the page somewhere, and use JavaScript to get the information from the DOM

This method is less preferable to AJAX, but it still has its advantages. It's still relatively separated between PHP and JavaScript in a sense that there is no PHP directly in the JavaScript.

Pros

• Fast - DOM operations are often quick, and you can store and access a lot of data relatively quickly.

Cons

• Potentially Unsemantic Markup - Usually, what happens is that you use some sort of <input type=hidden> to store the information, because it's easier to get the information out of inputNode.value, but doing so means that you have a meaningless element in your HTML. HTML has the <meta> element for data about the document, and HTML 5 introduces data-* attributes for data specifically for reading with JavaScript that can be associated with particular elements.
• Dirties up the Source - Data that PHP generates is outputted directly to the HTML source, meaning that you get a bigger and less focused HTML source.
• Harder to get structured data - Structured data will have to be valid HTML, otherwise you'll have to escape and convert strings yourself.
• Tightly couples PHP to your data logic - Because PHP is used in presentation, you can't separate the two cleanly.

Implementation Example

With this, the idea is to create some sort of element which will not be displayed to the user, but is visible to JavaScript.

index.php

<!-- snip -->
<div id="dom-target" style="display: none;">
    <?php
        $output = "42"; // Again, do some operation, get the output.
        echo htmlspecialchars($output); /* You have to escape because the result
                                           will not be valid HTML otherwise. */
    ?>
</div>
<script>
    var div = document.getElementById("dom-target");
    var myData = div.textContent;
</script>
<!-- snip -->

3. Echo the data directly to JavaScript

This is probably the easiest to understand.

Pros

• Very easily implemented - It takes very little to implement this, and understand.
• Does not dirty source - Variables are outputted directly to JavaScript, so the DOM is not affected.

Cons

• Tightly couples PHP to your data logic - Because PHP is used in presentation, you can't separate the two cleanly.

Implementation Example

Implementation is relatively straightforward:

<!-- snip -->
<script>
    var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
</script>
<!-- snip -->

Good luck!

Data transfer from JavaScript to PHP

You would have to make an AJAX call from JavaScript to a PHP script. That PHP script would save the screen resolution in the current session (you'll need to use sessions for this). A PHP script requested at a later point could then access the screen resolution as passed by the JavaScript snippet.

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 transfer data from javascript to php with OnChange

Use Ajax to send data from Javascript to PHP

function testEndpoint(){
        $.ajax({
            url: "https://path/to/your-php-script.php",
            type: "POST",
            crossDomain: true,
            data: {"txt_maq": $("#txt_maq").val()},
            dataType: "json",
            error: function(xhr, status, error){
                console.log("Error: " + error);
            },
            success: function(result, status, xhr){
                console.log(result);
            }
        });
}

testEndpoint();

At your PHP script your-php-script.php
You can use txt_maq as a POST variable:

$useTxtMag = $_POST['txt_maq'];

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>

Transfer data between JavaScript and PHP through JSON

1. no estas usando json para usar json debes adicionar la libreria jquery
2. you are not using Json, if you wanna use Json, you should add jquery library

html

<!-- change your button -->
    <button type="button" onclick="registroModificacion()">Convert</button>><
<!-- add at the end of yout page. you have to use jquery library -->
    <script src="https://code.jquery.com/jquery-3.5.1.min.js" ></script>
    <script>
        function registroModificacion(){
            //get values of your form by id
            const needed = $('#needed').val();
            const usd= $('#usd').val();
            $.ajax({
              url:'paginaEn.php',
              type:"POST",
              data: {needed:needed,usd:usd},
              success:function(r){
               alert(r);
              },
            })
        }
    </script>

paginaEn.php

<?php
    $usd= $_POST['usd'];
    $needed= $_POST['needed'];
    echo $needed." ".$usd;
?>

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