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Save gragland/2970ae543df237a07be1dbbf810f23fe to your computer and use it in GitHub Desktop.
import { useState } from 'react'; | |
// Usage | |
function App() { | |
// Similar to useState but first arg is key to the value in local storage. | |
const [name, setName] = useLocalStorage('name', 'Bob'); | |
return ( | |
<div> | |
<input | |
type="text" | |
placeholder="Enter your name" | |
value={name} | |
onChange={e => setName(e.target.value)} | |
/> | |
</div> | |
); | |
} | |
// Hook | |
function useLocalStorage(key, initialValue) { | |
// State to store our value | |
// Pass initial state function to useState so logic is only executed once | |
const [storedValue, setStoredValue] = useState(() => { | |
try { | |
// Get from local storage by key | |
const item = window.localStorage.getItem(key); | |
// Parse stored json or if none return initialValue | |
return item ? JSON.parse(item) : initialValue; | |
} catch (error) { | |
// If error also return initialValue | |
console.log(error); | |
return initialValue; | |
} | |
}); | |
// Return a wrapped version of useState's setter function that ... | |
// ... persists the new value to localStorage. | |
const setValue = value => { | |
try { | |
// Allow value to be a function so we have same API as useState | |
const valueToStore = | |
value instanceof Function ? value(storedValue) : value; | |
// Save state | |
setStoredValue(valueToStore); | |
// Save to local storage | |
window.localStorage.setItem(key, JSON.stringify(valueToStore)); | |
} catch (error) { | |
// A more advanced implementation would handle the error case | |
console.log(error); | |
} | |
}; | |
return [storedValue, setValue]; | |
} |
When using this hook in an application and over time changing the object that is managed it will still return the object from localstorage which will miss the newly added property.
For example on my first day I commit using this hook:
useLocalStorage("example", { test: "hello" })
I deploy this code.
The next day I change the usage of this hook:
useLocalStorage("example", { test: "hello", somethingNew: "this was just added" })
Because I have test: "hello"
in my storage, this won't return the initial value for somethingNew.
2 possible solutions:
- the consumer of this hook should change the storage key every time this is done
- change
return item ? JSON.parse(item) : initialValue;
toreturn item ? { ...initialValue, ...JSON.parse(item)} : initialValue;
There is also the problem when removing an attribute it will still return it, but this might be less problematic.
You can sync the state of localStorage between all tabs that application is opened.
My solution was:
import { useEffect, useState } from "react";
const useLocalStorage = (key, initialValue) => {
// State to store our value
// Pass initial state function to useState so logic is only executed once
const [storedValue, setStoredValue] = useState(() => {
if (typeof window === "undefined") {
return initialValue;
}
try {
// Get from local storage by key
const item = window.localStorage.getItem(key);
// Parse stored json or if none return initialValue
return item ? JSON.parse(item) : initialValue;
} catch (error) {
// If error also return initialValue
console.log(error);
return initialValue;
}
});
// Return a wrapped version of useState's setter function that ...
// ... persists the new value to localStorage.
const setValue = (value) => {
try {
// Allow value to be a function so we have same API as useState
const valueToStore =
value instanceof Function ? value(storedValue) : value;
// Save state
setStoredValue(valueToStore);
// Save to local storage
if (typeof window !== "undefined") {
window.localStorage.setItem(key, JSON.stringify(valueToStore));
}
} catch (error) {
// A more advanced implementation would handle the error case
console.log(error);
}
};
// Sync localStorage between tabs
useEffect(() => {
const listener = (e) => {
if (e.key === key) {
setStoredValue(JSON.parse(e.newValue));
}
};
window.addEventListener("storage", listener);
return () => {
window.removeEventListener("storage", listener);
};
}
, [
key,
initialValue,
]);
return [storedValue, setValue];
};
export default useLocalStorage;
Could we add a custom serialization/deserialization logic?
function useLocalStorage(key, initialValue, serialize = JSON.stringify, deserialize = JSON.parse) {
And use those functions instead of calling JSON.stringify
/JSON.parse
.
I think this implementation has a small flaw in that you are assuming
storedValue
is up to date when you callconst valueToStore = value instanceof Function ? value(storedValue) : value
Probably better to use
useEffect
with a dependency on the value ofuseState
and write the value there to localstorage instead.