added test for JSON.parse errors and updated the code to handle errors

Signed-off-by: Benjamin Strasser <bp.strasser@gmail.com>

Author: benjaminstrasser

src/lib/utils/localstorage-writable.ts

@@ -16,7 +16,13 @@ export const localStorageWritable = <T>(
 	defaultValue?: T
 ): LocalStorageWritable<T> => {
 	const storedValue = browser ? localStorage.getItem(localStorageKey) : null
-	const localStorageValue = storedValue !== null ? JSON.parse(storedValue) : null
+	const localStorageValue = (() => {
+		try {
+			return storedValue !== null ? JSON.parse(storedValue) : null
+		} catch {
+			return null
+		}
+	})()
 
 	const initialValue: T | null = localStorageValue ?? defaultValue ?? null
 

src/lib/utils/localstorage-writable.unit.test.ts

@@ -89,6 +89,25 @@ describe('localStorageWritable', () => {
 		expect(localStorage.getItem('testKey')).toBe(JSON.stringify(2))
 		expect(get(store)).toBe(2)
 	})
+
+	it('should initialize with default value if non-valid JSON is present in localStorage', () => {
+		localStorage.setItem('testKey', 'invalid-json')
+
+		const defaultValue = 'default'
+		const store = localStorageWritable('testKey', defaultValue)
+
+		expect(get(store)).toBe(defaultValue)
+		expect(localStorage.getItem('testKey')).toBe(JSON.stringify(defaultValue))
+	})
+
+	it('should initialize with null if no default value and non-valid JSON is present in localStorage', () => {
+		localStorage.setItem('testKey', 'invalid-json')
+
+		const store = localStorageWritable('testKey')
+
+		expect(get(store)).toBe(null)
+		expect(localStorage.getItem('testKey')).toBe(JSON.stringify(null))
+	})
 })
 
 describe('localStorageWritable with no browser', () => {