useRef
/*
A common use case is to access a child imperatively:
*/
function TextInputWithFocusButton() {
const inputEl = useRef(null);
const onButtonClick = () => {
// `current` points to the mounted text input element
inputEl.current.focus();
};
return (
<>
<input ref={inputEl} type="text" />
<button onClick={onButtonClick}>Focus the input</button>
</>
);
}useReducer
function init(initialCount) { return {count: initialCount};}
function reducer(state, action) {
switch (action.type) {
case 'increment':
return {count: state.count + 1};
case 'decrement':
return {count: state.count - 1};
case 'reset': return init(action.payload); default:
throw new Error();
}
}
function Counter({initialCount}) {
const [state, dispatch] = useReducer(reducer, initialCount, init); return (
<>
Count: {state.count}
<button
onClick={() => dispatch({type: 'reset', payload: initialCount})}> Reset
</button>
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}useContext
const value = useContext(MyContext);Copyright © 2021 Codeinu
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