javascript 32 lines · 6 steps

A React hook backed by the URL hash

useHashState mirrors a piece of state into the URL fragment so it survives reloads and stays shareable.

Explained by highlit
React Intermediate custom-hooks url-state event-listeners history-api state-sync
1function useHashState(key, defaultValue) {
2 const parse = () => {
3 const params = new URLSearchParams(window.location.hash.slice(1));
4 return params.has(key) ? params.get(key) : defaultValue;
5 };
6 
7 const [value, setValue] = React.useState(parse);
8 
9 React.useEffect(() => {
10 const onHashChange = () => setValue(parse());
11 window.addEventListener('hashchange', onHashChange);
12 return () => window.removeEventListener('hashchange', onHashChange);
13 }, [key]);
14 
15 const update = React.useCallback(
16 (next) => {
17 const params = new URLSearchParams(window.location.hash.slice(1));
18 if (next === defaultValue || next == null || next === '') {
19 params.delete(key);
20 } else {
21 params.set(key, next);
22 }
23 const hash = params.toString();
24 const url = hash ? `#${hash}` : window.location.pathname + window.location.search;
25 window.history.replaceState(null, '', url);
26 setValue(next ?? defaultValue);
27 },
28 [key, defaultValue]
29 );
30 
31 return [value, update];
32}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1The URL hash can act as a persistent, shareable store for lightweight UI state.
  2. 2Syncing external state into React means listening for its change events and cleaning the listener up.
  3. 3Removing a key when its value is the default keeps URLs clean rather than littered with defaults.

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