在$ .POST中传递数组/对象出错

我的javascript代码如下：

var configuration = [];

configuration["step 1"] = val1;
configuration["step 2"] = val2;
configuration["step 3"] = val3;
configuration["extraData"] = extra_data;        

var data = {
    action: 'configuration_save',
    config: configuration,
};

$.post(ajaxurl, data, function (response) {
    alert(response)
});

PHP中的$_POST['config'] 显示空白，在传递数组时我是否做错了？

PHP CODE

$current_user = wp_get_current_user();
$user_id = $current_user->ID;

add_user_meta( $user_id, "CONFIG", $_POST['config']);

use below updated one

    var main_configuration = [] ;
    var configuration = [];
    var configuration ={
           'step 1' :  val1,
           'step 2' :  val2,
           'step 3' : val3,
           'extraData' : extra_data
    };

    main_configuration.push(configuration);

    var data = {
            action: 'configuration_save',
            config: main_configuration,

            };
    $.post(ajaxurl, data, function (response) {

                alert(response)

    });