useffect compare previous value to current
//Custom Hook
function usePrevious(value) {
const ref = useRef();
useEffect(() => {
ref.current = value;
});
return ref.current;
}
// Use it in useEffect
const Component = (props) => {
const {receiveAmount, sendAmount } = props
const prevAmount = usePrevious(receiveAmount);
useEffect(() => {
if(prevAmount.receiveAmount !== receiveAmount) {
// process here
}
}, [receiveAmount])
}when to use previous state in useState
import React, { useState } from "react";
import ReactDOM from "react-dom";
function Counter() {
const [count, setCount] = useState(0);
return (
<div>
<h1>{count}</h1>
<button onClick={() => setTimeout(() => setCount(count + 1), 2000)}>
Delayed Counter (basic)
</button>
<button onClick={() => setTimeout(() => setCount(x => x + 1), 2000)}>
Delayed Counter (functional)
</button>
<button onClick={() => setCount(count + 1)}>Immediate Counter</button>
</div>
);
}
const rootElement = document.getElementById("root");
ReactDOM.render(<Counter />, rootElement);useRef for diffing
function usePrevious(value) {
const ref = useRef();
useEffect(() => {
ref.current = value;
});
return ref.current;
}Copyright © 2021 Codeinu
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