***
title: "Merge Strategies"
generated: true
---------------
## MergeOrdersStrategy
Merges both Orders. If the guest order contains items which are already in the
existing Order, the guest Order quantity will replace that of the existing Order.
```ts title="Signature"
class MergeOrdersStrategy implements OrderMergeStrategy {
merge(ctx: RequestContext, guestOrder: Order, existingOrder: Order) => MergedOrderLine[];
}
```
* Implements: [`OrderMergeStrategy`](/current/core/reference/typescript-api/orders/order-merge-strategy#ordermergestrategy)
## UseExistingStrategy
The guest order is discarded and the existing order is used as the active order.
```ts title="Signature"
class UseExistingStrategy implements OrderMergeStrategy {
merge(ctx: RequestContext, guestOrder: Order, existingOrder: Order) => MergedOrderLine[];
}
```
* Implements: [`OrderMergeStrategy`](/current/core/reference/typescript-api/orders/order-merge-strategy#ordermergestrategy)
## UseGuestIfExistingEmptyStrategy
If the existing order is empty, then the guest order is used. Otherwise the existing order is used.
```ts title="Signature"
class UseGuestIfExistingEmptyStrategy implements OrderMergeStrategy {
merge(ctx: RequestContext, guestOrder: Order, existingOrder: Order) => MergedOrderLine[];
}
```
* Implements: [`OrderMergeStrategy`](/current/core/reference/typescript-api/orders/order-merge-strategy#ordermergestrategy)
## UseGuestStrategy
Any existing order is discarded and the guest order is set as the active order.
```ts title="Signature"
class UseGuestStrategy implements OrderMergeStrategy {
merge(ctx: RequestContext, guestOrder: Order, existingOrder: Order) => MergedOrderLine[];
}
```
* Implements: [`OrderMergeStrategy`](/current/core/reference/typescript-api/orders/order-merge-strategy#ordermergestrategy)