## Update line item quantities

Use this method to change the quantity of a line item.

This method returns a `Promise` that resolves with an object containing the following fields:
* `type`: one of either `"success"` or `"error"`
* `session`: only populated when `type` is `"success"`. Contains a [Session](/js/custom_checkout/session_object) instance representing the updated state.
* `error`: only populated when `type` is `"error"`. Contains an object with a string `message` field which can be displayed to your customer.

**Syntax:** `actions.updateLineItemQuantity(...)`

- `options` (object) **required**
  Options for `updateLineItemQuantity`.

  - `lineItem` (string) **required**
    The [ID](/js/custom_checkout/session_object.md#custom_checkout_session_object-lineItems-id) of the line item to update.

  - `quantity` (integer) **required**
    The new quantity of the line item.

### Update line item quantities

```jsx
actions.updateLineItemQuantity({
  lineItem: 'LINE_ITEM_ID',
  quantity: 2,
});
```