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
const memoizedResult = useMemo(() => {
return expensiveFunction(propA, propB);
}, [propA, propB]);csv.dictreader example
import csv
with open('names.csv', 'w') as csvfile:
fieldnames = ['first_name', 'last_name']
writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
writer.writeheader()
writer.writerow({'first_name': 'Baked', 'last_name': 'Beans'})
writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})
writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})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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