useLocalStorage()

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

1import React from 'react'
2
3import useLocalStorage from './useLocalStorage'
4
5// Usage
6export default function Component() {
7  const [isDarkTheme, setDarkTheme] = useLocalStorage('darkTheme', true)
8
9  const toggleTheme = () => {
10    setDarkTheme(prevValue => !prevValue)
11  }
12
13  return (
14    <button onClick={toggleTheme}>
15      {`The current theme is ${isDarkTheme ? `dark` : `light`}`}
16    </button>
17  )
18}