How to display a $_SESSION variable in custom woocommerce checkout field?

I am able to verify by viewing the “Application” tab in the dev tools that my session variable has carried over to the checkout page; and I have the WC hook setup that allows me to change the “default”/value of the field I want to insert data into.

However, I am unable to get them to read each other.

add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );

function custom_override_checkout_fields( $fields ) {
     $fields['order']['order_comments']['label'] = "Custom Neon Details (If included)";
     $fields['order']['order_comments']['default'] = $_SESSION["customtext"];
     var_dump( $fields );
     return $fields;
}

As you can see from the attached image, my session variable is present on that page. How now, do I get it to add that session variable to $fields[‘order’][‘order_comments’][‘default’]?

Any help is appreciated! Thanks.

Answer

Use session_start(); before accessing the $_SESSION variable:

add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );
function custom_override_checkout_fields( $fields ) {

    session_start();

    $fields['order']['order_comments']['label'] = "Custom Neon Details (If included)";
    $fields['order']['order_comments']['default'] = $_SESSION["customtext"];
    var_dump( $fields );
    return $fields;
}

Alternatively you can use jQuery with sessionStorage:

// set the value of the order comment field via session storage
add_action( 'wp_footer', 'set_value_order_comments_field_via_session_storage' );
function set_value_order_comments_field_via_session_storage() {
    ?>
    <script type="text/javascript">
        jQuery(function($){
            var customtext = sessionStorage.getItem("customtext");
            if ( customtext.length ) {
                $('#order_comments').val(customtext);
            }
        });
    </script>
    <?php
}

The code has been tested and works. Add it to your active theme’s functions.php.