gristlabs_grist-core/app/client/lib/localStorageObs.ts

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import {Observable} from 'grainjs';
/**
* Returns true if storage is functional. In some cass (e.g. when embedded), localStorage may
* throw errors. If so, we return false. This implementation is the approach taken by store.js.
*/
function testStorage(storage: Storage) {
try {
const testStr = '__localStorage_test';
storage.setItem(testStr, testStr);
const ok = (storage.getItem(testStr) === testStr);
storage.removeItem(testStr);
return ok;
} catch (e) {
return false;
}
}
/**
* Returns localStorage if functional, or sessionStorage, or an in-memory storage. The fallbacks
* help with tests, and may help when Grist is embedded.
*/
export function getStorage(): Storage {
return _storage || (_storage = createStorage());
}
let _storage: Storage|undefined;
function createStorage(): Storage {
if (typeof localStorage !== 'undefined' && testStorage(localStorage)) {
return localStorage;
}
if (typeof sessionStorage !== 'undefined' && testStorage(sessionStorage)) {
return sessionStorage;
}
// Fall back to a Map-based implementation of (non-persistent) localStorage.
const values = new Map<string, string>();
return {
setItem(key: string, val: string) { values.set(key, val); },
getItem(key: string) { return values.get(key) ?? null; },
removeItem(key: string) { values.delete(key); },
clear() { values.clear(); },
get length() { return values.size; },
key(index: number): string|null { throw new Error('Not implemented'); },
};
}
/**
* Helper to create a boolean observable whose state is stored in localStorage.
*
* Optionally, a default value of true will make the observable start off as true. Note that the
* same default value should be used for an observable every time it's created.
*/
export function localStorageBoolObs(key: string, defValue = false): Observable<boolean> {
const store = getStorage();
const storedNegation = defValue ? 'false' : 'true';
const obs = Observable.create(null, store.getItem(key) === storedNegation ? !defValue : defValue);
obs.addListener((val) => val === defValue ? store.removeItem(key) : store.setItem(key, storedNegation));
return obs;
}
/**
* Helper to create a string observable whose state is stored in localStorage.
*/
export function localStorageObs(key: string, defaultValue?: string): Observable<string|null> {
const store = getStorage();
const obs = Observable.create<string|null>(null, store.getItem(key) ?? defaultValue ?? null);
obs.addListener((val) => (val === null) ? store.removeItem(key) : store.setItem(key, val));
return obs;
}