@statesync/svelte

---

@statesync/svelte / SvelteStoreSnapshotApplierOptions

Type Alias: SvelteStoreSnapshotApplierOptions<State, Data>

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

Defined in: svelte.ts:76

Configuration options for a Svelte store snapshot applier.

This union type provides correct return-type narrowing for toState depending on whether mode is 'patch' (returns Partial<State>) or 'replace' (returns full State).

Type Parameters

Type Parameter	Description
State extends Record<string, unknown>	The shape of the Svelte store value. 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 store shape.

Type Declaration

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

mode?

optional mode: "patch";

Apply mode.

• 'patch' -- shallow-merges mapped data into the current store value.

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. Use this to protect ephemeral/local-only fields (like UI flags) from being overwritten.

strict?

optional strict: boolean;

When true, throws an error if toState returns a non-plain-object value. When false, silently ignores the invalid return value.

Default Value

true

target?

optional target: "store";

Target kind. Omit or set to 'store' for Svelte 4 writable stores.

Default Value

'store'

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 target store. Return a partial object whose keys will be shallow-merged into the current value.

Parameters

Parameter	Type	Description
data	Data	The raw snapshot payload.
ctx	{ store: SvelteStoreLike<State>; }	Context providing access to the target store.
ctx.store	SvelteStoreLike<State>	-

Returns

Partial<State>

A partial state object to merge.

Default Value

Identity cast (data as Partial<State>).

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

mode

mode: "replace";

Apply mode.

• 'replace' -- replaces the entire store value atomically, removing keys not present in the mapped data (respecting key filters).

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?

optional target: "store";

Target kind. Omit or set to 'store' for Svelte 4 writable stores.

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	{ store: SvelteStoreLike<State>; }	Context providing access to the target store.
ctx.store	SvelteStoreLike<State>	-

Returns

State

The full next state.

Default Value

Identity cast (data as State).