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>
</>
);
}usememo hook react
const [a,setA]=useState(0);
const [b,setB]=useState(0);
const pow=(a)=>{
return Math.pow(a,2);
}
var val= useMemo(()=>{
return pow(a); // calling pow function using useMemo hook
},[a]); // only will be called once a will changed (for "a" we can maintain state)
return(
<input type="text" onChange={(e)=>{setA(e.target.value)}}>
<input type="text" onChange={(e)=>{setB(e.target.value)}}>
{val} // to access the value from useMemo
)useMemo
const memoizedResult = useMemo(() => {
return expensiveFunction(propA, propB);
}, [propA, propB]);useMemo
/*
Pass a “create” function and an array of dependencies.
useMemo will only recompute the memoized value when one
of the dependencies has changed. This optimization helps
to avoid expensive calculations on every render.
*/
const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);Copyright © 2021 Codeinu
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