我需要用PHP阅读ajax帖子

I am attempting to update a database using ajax and PHP. Right now, i am just testing to see if my receiving PHP file is getting the POST data by echoing it, but all I get back is an 'undefined index' error.

Here's my sending code:

var content = $(".homeContent").html();
                var dataString = "homepage|content|"+content;
                //var 
                $.ajax(
                        {

                        type: "POST",
                        url: "Update.php",
                        data: "dataString="+dataString,
                        success: function (result) {
                                console.log(dataString);
                        }
                });

and here is my receiving file (Update.php):

<?php
echo $_REQUEST['dataString'];
?>

Try this:

Ajax (JavaScript):

$.post( "Update.php", { dataString: "some String" } );

PHP:

<?php
echo $_POST['dataString'];
?>