33 lines
933 B
Plaintext
33 lines
933 B
Plaintext
/**
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* Copyright (c) 2015-present, Facebook, Inc.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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* @flow strict
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*/
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import isPromise from './isPromise';
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import type { MaybePromise } from './MaybePromise';
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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) => MaybePromise<U>,
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initialValue: MaybePromise<U>,
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): MaybePromise<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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