27 lines
1.3 KiB
JavaScript
27 lines
1.3 KiB
JavaScript
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import * as React from 'react';
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/**
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* Hook to initialize and return a constant value. Unlike `React.useMemo`, this is guaranteed to
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* always return the same value (and if the initializer is a function, only call it once).
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* This is similar to setting a private member in a class constructor.
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*
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* If the value should ever change based on dependencies, use `React.useMemo` instead.
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*
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* @param initialValue - Initial value, or function to get the initial value. Similar to `useState`,
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* only the value/function passed in the first time this is called is respected.
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* @returns The value. The identity of this value will always be the same.
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*/
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export function useConst(initialValue) {
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// Use useRef to store the value because it's the least expensive built-in hook that works here
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// (we could also use `const [value] = React.useState(initialValue)` but that's more expensive
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// internally due to reducer handling which we don't need)
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var ref = React.useRef();
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if (ref.current === undefined) {
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// Box the value in an object so we can tell if it's initialized even if the initializer
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// returns/is undefined
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ref.current = {
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value: typeof initialValue === 'function' ? initialValue() : initialValue,
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};
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}
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return ref.current.value;
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}
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//# sourceMappingURL=useConst.js.map
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