# Utilities <!-- omit in toc -->

## Table of Contents <!-- omit in toc -->

- [`extensionCartUpdate`](#extensioncartupdate)
   	- [`extensionCartUpdate` Usage](#extensioncartupdate-usage)
   	- [`extensionCartUpdate` Options](#extensioncartupdate-options)
      		- [`args (object, required)`](#args-object-required)
- [`mustContain`](#mustcontain)
   	- [`mustContain` Usage](#mustcontain-usage)
   	- [`mustContain` Options](#mustcontain-options)
      		- [`value (string, required)`](#value-string-required)
      		- [`requiredValue (string, required)`](#requiredvalue-string-required)

Miscellaneous utility functions for dealing with checkout functionality.

## `extensionCartUpdate`

When executed, this will call the cart/extensions REST API endpoint. The new cart is then received into the client-side store. `extensionCartUpdate` returns a promise that resolves when the cart is updated which should also be used for error handling.

### `extensionCartUpdate` Usage

```ts
// Aliased import
import { extensionCartUpdate } from '@woocommerce/blocks-checkout';

// Global import
// const { extensionCartUpdate } = wc.blocksCheckout;

extensionCartUpdate( {
	namespace: 'extension-unique-namespace',
	data: {
		key: 'value',
	},
} ).then( () => {
	// Cart has been updated.
} ).catch( ( error ) => {
	// Handle error.
} );
```

### `extensionCartUpdate` Options

The following options are available:

#### `args (object, required)`

Args to pass to the Rest API endpoint. This can contain data and a namespace to trigger extension specific functionality on the server-side. [You can read more about this, and the server-side implementation, in this doc.](../../../docs/third-party-developers/extensibility/rest-api/extend-rest-api-update-cart.md)

## `mustContain`

Ensures that a given value contains a string, or throws an error.

### `mustContain` Usage

```js
// Aliased import
import { mustContain } from '@woocommerce/blocks-checkout';

// Global import
// const { mustContain } = wc.blocksCheckout;

mustContain( 'This is a string containing a <price />', '<price />' ); // This will not throw an error
mustContain( 'This is a string', '<price />' ); // This will throw an error
```

### `mustContain` Options

The following options are available:

#### `value (string, required)`

Value being checked. Must be a string.

#### `requiredValue (string, required)`

What value must contain. If this is not found within `value`, and error will be thrown.

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