如何在jQuery中发送Array thru .post？

Here is my code that does not work:

var sessionListJSON = GatherSessionsFromPage();

    $.post('ajax.php', {
        _ExportMissingAddressesToXLS : 1,
        sessions : sessionListJSON  // ARRAY
    }, function(data) {

    }); 

here is my php attempt to catch it:

else if (array_key_exists('_ExportMissingAddressesToXLS', $_POST)) { // {{{
    $sessions = $_POST['sessions'];
    ExportMissingParentAddressesToXLS($sessions);
} // }}}

How do I properly send this array through this jQuery .post and then retrieve it in PHP? Also, would this be a case of serialization? If so, how do you do this for JS/jQuery?

jQuery automatically serializes arrays for you in $.post(). In PHP, $_POST['sessions'] will be an array if sessionListJSON was an array. You can access it with ordinary array indexing, foreach, etc.

If sessionListJSON is really a JSON string, you need to decode it in PHP:

$session = json_decode($_POST['sessions']);

My suggestion when working when any complex data structure being passed between javascript and PHP would be to use JSON serialization/deserialization and not rely on $_POST behavior at all.

This may look like this in javascript/jQuery.

var json = JSON.stringify({
   _ExportMissingAddressesToXLS : 1,
    sessions : sessionListJSON  // ARRAY
});
$.ajax({
    type: 'POST',
    url: 'ajax.php',
    contentType: 'application/json',
    dataType: 'json', // if you expect JSON in return
    data: json,  // your JSON string here
    success: // your success handler
    error: // your error handler
});

On the PHP-side, since you are not dealing with form-encoded data, you would need to read PHP's raw input. Luckily this is very simple and converting the POST data into a PHP object/array is very trivial. It is as simple as this:

$json = file_get_contents('php://input');
$variable = json_decode($json);

Note that with default json_decode() behavior you would actually get an object that you could work with like

if($variable->_ExportMissingAddressesToXLS === 1) {
     $sessions = $variable->sessions;
     ExportMissingParentAddressesToXLS($sessions);
}