@statesync/svelte

---

@statesync/svelte / SvelteStateSnapshotApplierOptions

Type Alias: SvelteStateSnapshotApplierOptions<State, Data>

type SvelteStateSnapshotApplierOptions<State, Data> = 
  | {
  mode?: "patch";
  omitKeys?: ReadonlyArray<keyof State>;
  pickKeys?: ReadonlyArray<keyof State>;
  strict?: boolean;
  target: "state";
  toState?: (data, ctx) => Partial<State>;
}
  | {
  mode: "replace";
  omitKeys?: ReadonlyArray<keyof State>;
  pickKeys?: ReadonlyArray<keyof State>;
  strict?: boolean;
  target: "state";
  toState?: (data, ctx) => State;
};

Defined in: svelte.ts:170

Configuration options for a Svelte 5 $state snapshot applier.

When target is 'state', the applier mutates the state proxy object in-place (property assignment / delete), which is how Svelte 5 fine-grained reactivity tracks changes. No new object reference is created.

Type Parameters

Type Parameter	Description
State extends Record<string, unknown>	The shape of the $state proxy object. Must be a plain object.
Data	The snapshot payload type received from the sync engine. Defaults to State when the snapshot maps 1:1 to the state shape.

Type Declaration

{
  mode?: "patch";
  omitKeys?: ReadonlyArray<keyof State>;
  pickKeys?: ReadonlyArray<keyof State>;
  strict?: boolean;
  target: "state";
  toState?: (data, ctx) => Partial<State>;
}

mode?

optional mode: "patch";

Apply mode.

• 'patch' -- assigns mapped properties onto the existing state proxy.

Default Value

'patch'

omitKeys?

optional omitKeys: ReadonlyArray<keyof State>;

Prevent these top-level keys from being updated by snapshots. Mutually exclusive with pickKeys.

pickKeys?

optional pickKeys: ReadonlyArray<keyof State>;

Allow only these top-level keys to be updated by snapshots. Mutually exclusive with omitKeys.

strict?

optional strict: boolean;

When true, throws an error if toState returns a non-plain-object value.

Default Value

true

target

target: "state";

Must be 'state' to opt into the Svelte 5 $state proxy target path.

toState()?

optional toState: (data, ctx) => Partial<State>;

Maps raw snapshot data to a partial state patch.

Receives the snapshot payload and a context object containing the current state proxy.

Parameters

Parameter	Type	Description
data	Data	The raw snapshot payload.
ctx	{ state: State; }	Context providing access to the current $state proxy.
ctx.state	State	-

Returns

Partial<State>

A partial state object whose properties will be assigned in-place.

Default Value

Identity cast (data as Partial<State>).

{
  mode: "replace";
  omitKeys?: ReadonlyArray<keyof State>;
  pickKeys?: ReadonlyArray<keyof State>;
  strict?: boolean;
  target: "state";
  toState?: (data, ctx) => State;
}

mode

mode: "replace";

Apply mode.

• 'replace' -- deletes keys not present in the mapped data, then assigns the new keys. Keys excluded by pickKeys / omitKeys are left untouched.

omitKeys?

optional omitKeys: ReadonlyArray<keyof State>;

Prevent these top-level keys from being updated by snapshots. Mutually exclusive with pickKeys.

pickKeys?

optional pickKeys: ReadonlyArray<keyof State>;

Allow only these top-level keys to be updated by snapshots. Mutually exclusive with omitKeys.

strict?

optional strict: boolean;

When true, throws an error if toState returns a non-plain-object value.

Default Value

true

target

target: "state";

Must be 'state' to opt into the Svelte 5 $state proxy target path.

toState()?

optional toState: (data, ctx) => State;

Maps raw snapshot data to a full next state.

When using 'replace' mode, prefer returning the complete state to avoid accidentally leaving stale keys.

Parameters

Parameter	Type	Description
data	Data	The raw snapshot payload.
ctx	{ state: State; }	Context providing access to the current $state proxy.
ctx.state	State	-

Returns

State

The full next state.

Default Value

Identity cast (data as State).