您根本不需要运行Ajax.WooCommerce在自动更改默认字段后刷新结帐页面.您需要以下代码:

You do not need to run Ajax at all. WooCommerce refreshes the checkout page after changing the default fields automatically. The following code is what you need:

add_action( 'woocommerce_review_order_before_submit', 'ywp_conditional_delivery_field' );
function ywp_conditional_delivery_field() {
    $state_code = 'VIC';

    if( $selected_state_code = WC()->customer->get_billing_state() ) {
        $country_code = WC()->customer->get_billing_country();
        $state_name   = WC()->countries->get_states( $country_code )[$state_code];

        if( WC()->customer->get_billing_state() === $state_code ) {
            $field_id           = 'my_datepicker';
            $today              = strtotime( 'today' );
            $tomorrow           = strtotime( 'tomorrow' );
            $dayAfterTomorrow   = strtotime( '+2 days' );

            woocommerce_form_field( $field_id, array(
                'type'          => 'select',
                'class'         => array( 'form-row-wide' ),
                'label'         => __( 'Delivery Date For Victoria' ),
                'placeholder'   => __( 'Select Delivery Date For Victoria' ),
                'required'      => true, // Or false
                'options'       => array(
                    ''                          => 'Select',
                    date( ( 'd F Y' ), $today )     => date( ( 'd F Y' ), $today ),
                    date( ( 'd F Y' ), $tomorrow ) => date( ( 'd F Y' ), $tomorrow ),
                )
            ) );
        } else {
            woocommerce_form_field(  $field_id, array(
                'type'          => 'select',
                'class'         => array( 'form-row-wide' ),
                'label'         => __( 'Delivery Date' ),
                'placeholder'   => __( 'Select Delivery Date' ),
                'required'      => true, // Or false
                'options'       => array(
                    '' => 'Select',
                    date( ( 'd F Y' ), $tomorrow ) => date( ( 'd F Y' ), $tomorrow ),
                    date( ( 'd F Y' ), $dayAfterTomorrow ) => date( ( 'd F Y' ), $dayAfterTomorrow ),
                )
            ));
        }
    }
}

编辑

以下代码可以正常工作，以在您需要的订单注释前显示发货日期:

The following code works correctly to display the shipping date before the order note that you need it:

add_action( 'woocommerce_before_order_notes', 'ywp_conditional_delivery_field' );
function ywp_conditional_delivery_field() {
    $today              = date( 'd F Y' ,strtotime( 'today' ) );
    $tomorrow           = date( 'd F Y' ,strtotime( 'tomorrow' ) );
    $dayAfterTomorrow   = date( 'd F Y' ,strtotime( '+2 days' ) );
    ?>
    <script>
        jQuery(document).ready(function($){
            $('#billing_state').on('change',function(){
                if($(this).val()=='VIC'){
                    $('#my_non_VIC_datepicker_field').remove();
                    $('#order_comments_field').prepend('<p class="form-row form-row-wide validate-required" id="my_VIC_datepicker_field" data-priority=""><label for="my_VIC_datepicker" class="">Delivery Date For Victoria&nbsp;<abbr class="required" title="required">*</abbr></label><span class="woocommerce-input-wrapper"><select name="my_VIC_datepicker" id="my_VIC_datepicker" class="select " data-allow_clear="true" data-placeholder="Select Delivery Date For Victoria"><option value=""  selected="selected">Select</option><option value="<?php echo $today; ?>" ><?php echo $today; ?></option><option value="<?php echo $tomorrow; ?>"><?php echo $tomorrow; ?></option></select></span></p>');
                } else {
                    $('#my_VIC_datepicker_field').remove();
                    $('#order_comments_field').prepend('<p class="form-row form-row-wide validate-required" id="my_non_VIC_datepicker_field" data-priority=""><label for="my_non_VIC_datepicker_field" class="">Delivery Date&nbsp;<abbr class="required" title="required">*</abbr></label><span class="woocommerce-input-wrapper"><select name="my_non_VIC_datepicker" id="my_non_VIC_datepicker" class="select " data-allow_clear="true" data-placeholder="Select Delivery Date"><option value=""  selected="selected">Select</option><option value="<?php echo $today; ?>" ><?php echo $today; ?></option><option value="<?php echo $tomorrow; ?>"><?php echo $tomorrow; ?></option><option value="<?php echo $dayAfterTomorrow; ?>"><?php echo $dayAfterTomorrow; ?></option></select></span></p>');
                }
            });
        })
    </script>
    <?php
}

代码进入活动主题/子主题的 functions.php 中.经过测试，可以正常工作.

Code goes in functions.php of your active theme/child theme. Tested and works.