66 lines
2.0 KiB
Markdown
66 lines
2.0 KiB
Markdown
---
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title: useAsync
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tags: hooks,state,reducer,advanced
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---
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A hook that handles asynchronous calls.
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- Create a custom hook that takes a handler function, `fn`.
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- Define a reducer function and an initial state for the custom hook's state.
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- Use the `React.useReducer()` hook to initialize the `state` variable and the `dispatch` function.
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- Define a `run` function that will run the provided callback, `fn`, while using `dispatch` to update `state` as necessary.
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- Return an object containting the the properties of `state` (`value`, `error` and `loading`) and the `run` function.
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```jsx
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const useAsync = (fn) => {
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const initialState = { loading: false, error: null, value: null };
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const stateReducer = (_, action) => {
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switch (action.type) {
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case 'start':
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return { loading: true, error: null, value: null};
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case 'finish':
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return { loading: false, error: null, value: action.value};
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case 'error':
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return { loading: false, error: action.error, value: null};
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}
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}
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const [state, dispatch] = React.useReducer(stateReducer, initialState);
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const run = async (args = null) => {
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try {
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dispatch({ type: 'start' });
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const value = await fn(args);
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dispatch({ type: 'finish', value });
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} catch (error) {
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dispatch({ type: 'error', error });
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}
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};
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return { ...state, run };
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};
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```
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```jsx
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const RandomImage = props => {
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const imgFetch = useAsync(url => fetch(url).then(response => response.json()));
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return (
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<div>
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<button
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onClick={() => imgFetch.run('https://dog.ceo/api/breeds/image/random')}
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disabled={ imgFetch.isLoading }
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>
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Load image
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</button>
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<br/>
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{ imgFetch.loading && <div>Loading...</div> }
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{ imgFetch.error && <div>Error { imgFetch.error }</div> }
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{ imgFetch.value && <img src={ imgFetch.value.message } alt="avatar" width={400} height="auto" />}
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</div>
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);
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};
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ReactDOM.render(<RandomImage />, document.getElementById('root'));
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```
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