Filters

Like traditional WordPress filters (you register a callback with a specific filter, your callback accepts a number of arguments, then it returns a value), we are introducing filters to the WooCommerce Blocks extension. These will function very similarly to the traditional filters.

Your extension will use __experimentalRegisterCheckoutFilter to set up a filter.

This function has the following signature:

(
  namespace: string,
  filters: Record< string, CheckoutFilterFunction >
)

and a CheckoutFilterFunction has this signature:

type CheckoutFilterFunction = < T >(
	value: T,
	extensions: Record< string, unknown >,
	args?: CheckoutFilterArguments
) => T;

In this, you'll specify which filter you want to work with (available filters are listed below) and the function (CheckoutFilterFunction) to execute when this filter is applied.

When the CheckoutFilterFunction is invoked, the following arguments are passed to it:

value - The value to be filtered.
extensions A n object containing extension data. If your extension has extended any of the store's API routes, one of the keys of this object will be your extension's namespace. The value will contain any data you add to the endpoint. Each key in the extensions object is an extension namespace, so a third party extension cannot interfere with your extension's schema modifications, unless there is a naming collision, so please ensure your extension has a unique namespace that is unlikely to conflict with other extensions.
args - An object containing any additional data passed to the filter function. This usually (but not always) contains at least a key called context. The value of context will be (at the moment) either cart or checkout. This is provided to inform extensions about the exact location that the filter is being applied. The same filter can be applied in multiple places.

Available filters

This section of the document will list the filters that are currently available to extensions, where exactly the filter is applied, and what data might be passed to the CheckoutFilterFunction.

Cart Line Items

Line items refers to each item listed in the cart or checkout. For instance the "Sunglasses" and "Beanie with logo" in this image are the line items.

The following filters are available for line items:

Filter name	Description	Return type
`itemName`	Used to change the name of the item before it is rendered onto the page	`string`
`cartItemPrice`	This is the price of the item, multiplied by the number of items in the cart.	`string` and must contain the substring `<price/>` where the price should appear.
`subtotalPriceFormat`	This is the price of a single item. Irrespective of the number in the cart, this value will always be the current price of one item.	`string` and must contain the substring `<price/>` where the price should appear.
`saleBadgePriceFormat`	This is amount of money saved when buying this item. It is the difference between the item's regular price and its sale price.	`string` and must contain the substring `<price/>` where the price should appear.

Each of these filters has the following arguments passed to it: { context: 'cart', cartItem: CartItem } (CartItem)

Order Summary Items

In the Checkout block, there is a sidebar that contains a summary of what the customer is about to purchase. There are some filters available to modify the way certain elements are displayed on each item.

The sale badges are not shown here, so those filters are not applied in the Order Summary.

Filter name	Description	Return type
`itemName`	Used to change the name of the item before it is rendered onto the page	`string`
`cartItemPrice`	This is the price of the item, multiplied by the number of items in the cart.	`string` and must contain the substring `<price/>` where the price should appear.
`subtotalPriceFormat`	This is the price of a single item. Irrespective of the number in the cart, this value will always be the current price of one item.	`string` and must contain the substring `<price/>` where the price should appear.

Each of these filters has the following additional arguments passed to it: { context: 'summary', cartItem: CartItem } (CartItem)

Totals footer item (in Cart and Checkout)

The word 'Total' that precedes the amount due, present in both the Cart and Checkout blocks, is also passed through filters.

Filter name	Description	Return type
`totalLabel`	This is the label for the cart total. It defaults to 'Total' (or the word for 'Total' if using translations).	`string`

There are no additional arguments passed to this filter.

Coupons

The current functionality is to display the coupon codes in the Cart and Checkout sidebars. This could be undesirable if you dynamically generate a coupon code that is not user-friendly. It may, therefore, be desirable to change the way this code is displayed. To do this, the filter couponName exists.

This filter could also be used to show or hide coupons.

This filter must not be used to alter the value/totals of a coupon. This will not carry through to the Cart totals.

Filter name	Description	Return type
`coupons`	This is an array of coupons currently applied to the cart.	`CartCoupon[]`

The additional argument supplied to this filter is: { context: 'summary' }. A CartCoupon has the following shape:

CartCoupon {
  code: string
  discount_type: string
  totals: {
    currency_code: string
    currency_decimal_separator: string
    currency_minor_unit: number
    currency_prefix: string
    currency_suffix: string
    currency_symbol: string
    currency_thousand_separator: string
    total_discount: string
    total_discount_tax: string
  }
}

Examples

Changing the wording of the Totals label in the Cart and Checkout

For this example, let's suppose we are building an extension that lets customers pay a deposit, and defer the full amount until a later date.

To make it easier to understand what the customer is paying and why, let's change the value of Total to Deposit due today.

We need to create a CheckoutFilterFunction.

const replaceTotalWithDeposit = () => 'Deposit due today';

Now we need to register this filter function, and have it executed when the totalLabel filter is applied. We can access the __experimentalRegisterCheckoutFilters function on the window.wc.blocksCheckout object. As long as your extension's script is enqueued after WooCommerce Blocks' scripts (i.e. by registering wc-blocks-checkout as a dependency), then this will be available.

const { __experimentalRegisterCheckoutFilters } = window.wc.blocksCheckout;
__experimentalRegisterCheckoutFilters( 'my-hypothetical-deposit-plugin', {
 totalLabel: replaceTotalWithDeposit
} );

Before	After

Changing the format of the item's single price

Let's say we want to add a little bit of text after an item's single price in the Cart only, just to make sure our customers know that's the price per item.

We will need to register a function to be executed when the subtotalPriceFormat is applied. Since we only want this to happen in the Cart context, our function will need to check the additional arguments passed to it to ensure the context value is cart.

We can see from the table above, that our function needs to return a string that contains a substring of <price/>. This is a placeholder for the numeric value. The Cart block will interpolate the value into the string we return.

const appendTextToPriceInCart = ( value, extensions, args ) => {
  if( args?.context !== 'cart') {
      // Return early since this filter is not being applied in the Cart context.
      // We must return the original value we received here.
      return value;
  }
  return '<price/> per item';
};

Now we must register it. Refer to the first example for information about __experimentalRegisterCheckoutFilters.

const { __experimentalRegisterCheckoutFilters } = window.wc.blocksCheckout;
__experimentalRegisterCheckoutFilters( 'my-hypothetical-price-plugin', {
  subtotalPriceFormat: appendTextToPriceInCart
} );

Before	After

Troubleshooting

If you are logged in to the store as an administrator, you should be shown an error like this if your filter is not working correctly.

The error will also be shown in your console.

woocommerce-blocks/docs/extensibility/available-filters.md