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26 lines
759 B
26 lines
759 B
// @flow strict
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import type { PromiseOrValue } from './PromiseOrValue';
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import isPromise from './isPromise';
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/**
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* Similar to Array.prototype.reduce(), however the reducing callback may return
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* a Promise, in which case reduction will continue after each promise resolves.
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*
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* If the callback does not return a Promise, then this function will also not
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* return a Promise.
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*/
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export default function promiseReduce<T, U>(
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values: $ReadOnlyArray<T>,
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callback: (U, T) => PromiseOrValue<U>,
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initialValue: PromiseOrValue<U>,
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): PromiseOrValue<U> {
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return values.reduce(
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(previous, value) =>
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isPromise(previous)
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? previous.then((resolved) => callback(resolved, value))
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: callback(previous, value),
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initialValue,
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);
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}
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