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useMap react Code Snippet in 2022

hooksstateadvanced

Last Updated: 25 September 2022

Creates a stateful Map object, and a set of functions to manipulate it.

  • Use the useState() hook and the Map constructor to create a new Map from the initialValue.
  • Use the useMemo() hook to create a set of non-mutating actions that manipulate the map state variable, using the state setter to create a new Map every time.
  • Return the map state variable and the created actions.
const useMap = initialValue => { const [map, setMap] = React.useState(new Map(initialValue)); const actions = React.useMemo( () => ({ set: (key, value) => setMap(prevMap => { const nextMap = new Map(prevMap); nextMap.set(key, value); return nextMap; }), remove: (key, value) => setMap(prevMap => { const nextMap = new Map(prevMap); nextMap.delete(key, value); return nextMap; }), clear: () => setMap(new Map()), }), [setMap] ); return [map, actions]; };
const MyApp = () => { const [map, { set, remove, clear }] = useMap([['apples', 10]]); return ( <div> <button onClick={() => set(Date.now(), new Date().toJSON())}>Add</button> <button onClick={() => clear()}>Reset</button> <button onClick={() => remove('apples')} disabled={!map.has('apples')}> Remove apples </button> <pre> {JSON.stringify( [...map.entries()].reduce( (acc, [key, value]) => ({ ...acc, [key]: value }), {} ), null, 2 )} </pre> </div> ); }; ReactDOM.render(<MyApp />, document.getElementById('root'));

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