You will need to store the data somewhere. You COULD write to a text file. This is terrible in practice. The best thing to do here is use a database.

Once the PHP renders the page, it's done, no more changes there. To update the page in real-time, you need to use JavaScript (you can use the success function of your ajax call to do it). However, to make this work for all the users, you need to keep the value of that variable somewhere - a database, or even a textfile. Database is strongly recommended. After all, that's what they are meant for.

Your ajax call needs to call a PHP function that will increase that value for you and probably echo something to denote whether it was successful. Upon that returned result, you update the existing page by using the success function, like I mentioned above.

You can do this without a database — you could store the value in memory (memcache, redis) or a flat file.

However, an in-memory store isn't going to persist across crashes or reboots, and a file-based solution could result in hangs or delays, as only one client can have write access to the file at a time.

Why don't you want to use a database? If you don't have MySQL access, you could try sqlite.

You can temporarily store the data in $_SESSION (http://php.net/manual/en/features.sessions.php) or in a cookie (http://php.net/manual/en/features.cookies.php). You cannot store this data permanently without a database.

There are threetwo ways to do this without database.

file storage

store the value of variable in a file using file_put_contents and retrieve it using file_get_contents, increase by ten and save it again in the same file.

serialize or export

using functions var_export() or serialize() , you can store variables and arrays in files. Serialization and unserialization is more resource intensive but in terms of storage space, its more effective than exporting.

Example:

<?php
include 'data.php';
$data[$_POST['itemid']]  += 10;
$towrite = var_export($data, true); 
file_put_contents('data.php',$towrite);
?>

and here is what data.php should look like before executing the above code:

<?php
 $data = array( 'myitemid' => 0);
?>

just replace myitemid with the unique identifier the like button is on.

Some options:

Option: You can use input field to store the value temporary, its faster than filesystem manipulation and do not have size limit.

Another Option: other option is using innerHTML of a div or another html element, i prefer input field because is easy to serialize and use in another ajax event and than its easy to persists. For example using json is fast and easy to save in MongoDB.

Example using input:

javascript example:

$('.classname a').click(function(e){
        $.ajax({
            url : '/foo',
            type: "POST",
            data: $("form.bar").serialize(),
            error: function(){
            },
            success : function(data){
                $('.input_class_name').val(
parseInt($('.input_class_name').val())+parteInt($('.another_input_class_name').val())
);
            }
        });
    });

html example( with 2 forms, using like this you can submit in diferent moments or put in the same form):

<form class="foo1">
<input type="hidden" class="another_input_class_name" value="10" />
</form>

<form class="bar">
<input type="hidden" class="input_class_name" value="10" />
</form>