useLocalStorage()

1import {
2  Dispatch,
3  SetStateAction,
4  useCallback,
5  useEffect,
6  useState,
7} from 'react'
8
9import { useEventCallback, useEventListener } from 'usehooks-ts'
10
11declare global {
12  interface WindowEventMap {
13    'local-storage': CustomEvent
14  }
15}
16
17type SetValue<T> = Dispatch<SetStateAction<T>>
18
19function useLocalStorage<T>(key: string, initialValue: T): [T, SetValue<T>] {
20  // Get from local storage then
21  // parse stored json or return initialValue
22  const readValue = useCallback((): T => {
23    // Prevent build error "window is undefined" but keeps working
24    if (typeof window === 'undefined') {
25      return initialValue
26    }
27
28    try {
29      const item = window.localStorage.getItem(key)
30      return item ? (parseJSON(item) as T) : initialValue
31    } catch (error) {
32      console.warn(`Error reading localStorage key “${key}”:`, error)
33      return initialValue
34    }
35  }, [initialValue, key])
36
37  // State to store our value
38  // Pass initial state function to useState so logic is only executed once
39  const [storedValue, setStoredValue] = useState<T>(readValue)
40
41  // Return a wrapped version of useState's setter function that ...
42  // ... persists the new value to localStorage.
43  const setValue: SetValue<T> = useEventCallback(value => {
44    // Prevent build error "window is undefined" but keeps working
45    if (typeof window === 'undefined') {
46      console.warn(
47        `Tried setting localStorage key “${key}” even though environment is not a client`,
48      )
49    }
50
51    try {
52      // Allow value to be a function so we have the same API as useState
53      const newValue = value instanceof Function ? value(storedValue) : value
54
55      // Save to local storage
56      window.localStorage.setItem(key, JSON.stringify(newValue))
57
58      // Save state
59      setStoredValue(newValue)
60
61      // We dispatch a custom event so every useLocalStorage hook are notified
62      window.dispatchEvent(new Event('local-storage'))
63    } catch (error) {
64      console.warn(`Error setting localStorage key “${key}”:`, error)
65    }
66  })
67
68  useEffect(() => {
69    setStoredValue(readValue())
70    // eslint-disable-next-line react-hooks/exhaustive-deps
71  }, [])
72
73  const handleStorageChange = useCallback(
74    (event: StorageEvent | CustomEvent) => {
75      if ((event as StorageEvent)?.key && (event as StorageEvent).key !== key) {
76        return
77      }
78      setStoredValue(readValue())
79    },
80    [key, readValue],
81  )
82
83  // this only works for other documents, not the current one
84  useEventListener('storage', handleStorageChange)
85
86  // this is a custom event, triggered in writeValueToLocalStorage
87  // See: useLocalStorage()
88  useEventListener('local-storage', handleStorageChange)
89
90  return [storedValue, setValue]
91}
92
93export default useLocalStorage
94
95// A wrapper for "JSON.parse()"" to support "undefined" value
96function parseJSON<T>(value: string | null): T | undefined {
97  try {
98    return value === 'undefined' ? undefined : JSON.parse(value ?? '')
99  } catch {
100    console.log('parsing error on', { value })
101    return undefined
102  }
103}

1import { useLocalStorage } from 'usehooks-ts'
2
3// Usage
4export default function Component() {
5  const [isDarkTheme, setDarkTheme] = useLocalStorage('darkTheme', true)
6
7  const toggleTheme = () => {
8    setDarkTheme((prevValue: boolean) => !prevValue)
9  }
10
11  return (
12    <button onClick={toggleTheme}>
13      {`The current theme is ${isDarkTheme ? `dark` : `light`}`}
14    </button>
15  )
16}