<div id="ShowPageContent">
    <a href="openpage.php?page=1" class="loadwithajax" data-page-link="index.php">Open Page One</a>
    <a href="openpage.php?page=2" class="loadwithajax" data-page-link="index.php">Open Page Two</a>
    <a href="openpage.php?page=3" class="loadwithajax" data-page-link="index.php">Open Page Three</a>
</div>

<script>
$(function(){
    "use strict";
    $(document).on('click', '.loadwithajax', function(e){
       var targetUrl = e.target.href;
       var prevUrl = $(this).attr('data-page-link');
        $.ajax({
            type: "POST",
            url: targetUrl,
            data: {targetUrl : targetUrl, prevUrl : prevUrl},
            async: false,
            beforeSend: function(){},
            success: function(htmlBlock){
               $('#ShowPageContent').html(htmlBlock);
           }
        });
        e.preventDefault();
    });
});
</script>

<?php
 $validateForm = 'validate-form-'.md5($_GET['targetUrl']);
?>
<a href="<?php echo $_GET['prevUrl'];?>" class="loadwithajax" data-page-link="">Back To Main Page</a>
<form action="" method="post" class="<?php echo $validateForm;?>">
    <input type="text" value=""/>
    <input type="submit" value="Send"/>
</form>

<script>
$(function(){
    "use strict";
    $(document).on('submit', '.<?php echo $validateForm;?>', function(e){
        $.ajax({
            type: "POST",
            url: ajax_appserver('shop', 'update_product.php'),
            data: $(self).serialize(),
            beforeSend: function(){},
            success: function(data){
               console.log(data);
           }
        });
        e.preventDefault();
    });
});
</script>