Persistent State in React

Persistent State in React

Posted on 26th May 2020

Sometimes we need to preserve the state in a React app in cases where we close the browser or reload the page. In this guide I’ll show you a simple custom hook to store the state in localstorage.

This guide will not work as is in frameworks like Next.js or Gatsby because the components aren't first rendered in the browser and localstorage can't be accessed. If you want to learn more about how rendering differs in the browser and the server check out this awesome post.

First create a function called useStickyState with the initial state (initialState) as an argument.

jsx
import React from "react";
const useStickyState = (initialState = null) => {};

Then let’s initialize the state and return it and the function to change it.

jsx
import React from "react";
const useStickyState = (initialState = null) => {
const [state, useState] = React.useState(initialState);
return [state, setState];
};

Next we’ll add an effect to store the state in localstorage when the state changes. Since we need an key to store a value in local storage we’ll add one as an argument.

jsx
import React from "react";
const useStickyState = (key = "sticky", initialState = null) => {
const [state, useState] = React.useState(initialState);
React.useEffect(() => {
localStorage.setItem(key, state);
}, [state]);
return [state, setState];
};

In its current form the state will always initialize with initialState, but we need to load the state from localstorage if available. We can use lazy initialization to check localstorage and use it’s value if present. If not, use initialState instead.

jsx
import React from "react";
const useStickyState = (key = "sticky", initialState = null) => {
const [state, setState] = React.useState(() => {
const storedState = localStorage.getItem(key);
return storedState ?? initialState;
});
React.useEffect(() => {
localStorage.setItem(key, state);
}, [state]);
return [state, setState];
};

To finish up the hook, let’s add and return a function to remove clear up the value in localstorage.

jsx
import React from "react";
const useStickyState = (key = "sticky", initialState = null) => {
const [state, setState] = React.useState(() => {
const storedState = localStorage.getItem(key);
return storedState ?? initialState;
});
React.useEffect(() => {
localStorage.setItem(key, state);
}, [state]);
const clearState = () => localStorage.removeItem(key);
return [state, setState, clearState];
};

Wrapping up

Below is an example on how to use the useStickyState hook to save the value in an <input>

jsx
import React from "react";
const useStickyState = (key = "sticky", initialState = null) => {
const [state, setState] = React.useState(() => {
const storedState = localStorage.getItem(key);
return storedState ?? initialState;
});
React.useEffect(() => {
localStorage.setItem(key, state);
}, [state]);
const clearState = () => localStorage.removeItem(key);
return [state, setState, clearState];
};
export default function App() {
const [value, setValue, clearValue] = useStickyState(
"sticky",
"Hello World!!!"
);
return (
<div className="App">
<h1>{`Value : ${value}`}</h1>
<input
type="text"
value={value}
onChange={(e) => setValue(e.target.value)}
/>
<button onClick={() => clearValue()}>Clear</button>
</div>
);
}

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