Adding data to the block Cart and Checkout with the Store API

WooCommerce’s block Cart and Checkout run on the Store API, not on PHP templates. Hooks such as woocommerce_review_order_before_payment don’t fire on these pages.

01Register extra data on the cart endpoint#

woocommerce_store_api_register_endpoint_data( [
    'endpoint'        => \Automattic\WooCommerce\StoreApi\Schemas\V1\CartSchema::IDENTIFIER,
    'namespace'       => 'hamidarab-delivery',
    'data_callback'   => static fn () => [ 'window' => get_delivery_window() ],
    'schema_callback' => static fn () => [
        'window' => [ 'type' => 'string', 'readonly' => true ],
    ],
    'schema_type'     => ARRAY_A,
] );

The data appears in the Store API response under extensions.hamidarab-delivery and is available on the JavaScript side.

02Show it in the UI#

Use Slot/Fill or an inner Checkout block to render it; jQuery DOM manipulation on these pages is fragile.

03What to test#

• Inspect the /wp-json/wc/store/v1/cart response directly.
• Test guest and logged-in customers separately.
• Check behaviour behind page cache and CDN; the Store API must never be cached.