| 1 | import { useEffect, useRef } from 'react';
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| 2 | /**
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| 3 | * Store the last of some value. Tracked via a `Ref` only updating it
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| 4 | * after the component renders.
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| 5 | *
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| 6 | * Helpful if you need to compare a prop value to it's previous value during render.
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| 7 | *
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| 8 | * ```ts
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| 9 | * function Component(props) {
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| 10 | * const lastProps = usePrevious(props)
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| 11 | *
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| 12 | * if (lastProps.foo !== props.foo)
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| 13 | * resetValueFromProps(props.foo)
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| 14 | * }
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| 15 | * ```
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| 16 | *
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| 17 | * @param value the value to track
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| 18 | */
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| 19 |
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| 20 | export default function usePrevious(value) {
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| 21 | var ref = useRef(null);
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| 22 | useEffect(function () {
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| 23 | ref.current = value;
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| 24 | });
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| 25 | return ref.current;
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| 26 | } |
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