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feat(PerststedState): Add .reset, remove key if set to undefined #392

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20 changes: 19 additions & 1 deletion packages/runed/src/lib/utilities/persisted-state/persisted-state.svelte.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,7 @@ function proxy<T>(
* @see {@link https://runed.dev/docs/utilities/persisted-state}
*/
export class PersistedState<T> {
#initial: T;
#current: T | undefined;
#key: string;
#serializer: Serializer<T>;
Expand All @@ -118,7 +119,7 @@ export class PersistedState<T> {
} = options;
const window = "window" in options ? options.window : defaultWindow; // window is not mockable to be undefined without this, because JavaScript will fill undefined with `= default`

this.#current = initialValue;
this.#initial = this.#current = initialValue;
this.#key = key;
this.#serializer = serializer;
this.#connected = connected;
Expand Down Expand Up @@ -168,6 +169,20 @@ export class PersistedState<T> {
this.#update?.();
}

/**
* Resets the state back to the initial value provided to the constructor.
*
* When connected to storage, an initial value of `undefined` results in the key
* being removed from storage.
* (If the initial value is `null`, it will be persisted as the string `"null"`
* by the default JSON serializer.)
*/
reset() {
this.#current = this.#initial;
this.#serialize(this.#initial);
this.#update?.();
}

#handleStorageEvent = (event: StorageEvent): void => {
if (event.key !== this.#key || event.newValue === null) return;
this.#current = this.#deserialize(event.newValue);
Expand All @@ -193,6 +208,9 @@ export class PersistedState<T> {
try {
if (value !== undefined) {
this.#storage?.setItem(this.#key, this.#serializer.serialize(value));
} else {
this.#current = value;
this.#storage?.removeItem(this.#key);
}
} catch (error) {
console.error(
Expand Down
30 changes: 30 additions & 0 deletions packages/runed/src/lib/utilities/persisted-state/persisted-state.test.svelte.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,36 @@ describe("PersistedState", async () => {
expect(persistedState.current).toBe(initialValue);
});

testWithEffect("removes the key when set to undefined", () => {
const persistedState = new PersistedState<string | undefined>(key, initialValue);
expect(localStorage.getItem(key)).toBe(JSON.stringify(initialValue));

persistedState.current = undefined;
expect(persistedState.current).toBeUndefined();
expect(localStorage.getItem(key)).toBeNull();
});

testWithEffect("reset restores the initial value after modifications", () => {
const persistedState = new PersistedState(key, initialValue);
persistedState.current = newValue;
expect(persistedState.current).toBe(newValue);
expect(localStorage.getItem(key)).toBe(JSON.stringify(newValue));

persistedState.reset();
expect(persistedState.current).toBe(initialValue);
expect(localStorage.getItem(key)).toBe(JSON.stringify(initialValue));
});

testWithEffect("reset removes the key if initial value is undefined", () => {
localStorage.setItem(key, JSON.stringify(existingValue));
const persistedState = new PersistedState<string | undefined>(key, undefined);
expect(localStorage.getItem(key)).toBe(JSON.stringify(existingValue));

persistedState.reset();
expect(persistedState.current).toBeUndefined();
expect(localStorage.getItem(key)).toBeNull();
});

testWithEffect("uses persisted value if it is found", () => {
localStorage.setItem(key, JSON.stringify(existingValue));
const persistedState = new PersistedState(key, initialValue);
Expand Down
22 changes: 22 additions & 0 deletions sites/docs/src/content/utilities/persisted-state.md
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,28 @@ Initialize `PersistedState` by providing a unique key and an initial value for t
</div>
```

### Reset

You can reset back to the initial value passed to the constructor:

```ts
const state = new PersistedState("count", 0);

state.current = 123;
state.reset();
console.log(state.current); // 0
```

### Clearing persisted storage

When connected to storage, setting `current` to `undefined` removes the key from storage:

```ts
const state = new PersistedState<string | undefined>("draft", "hello");

state.current = undefined; // removes "draft" from storage
```

### Complex objects

When persisting complex objects, only plain structures are deeply reactive.
Expand Down