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Dan Abramov
45c1ff348e
* Remove use strict from ES modules * Delete unused file This was unused since Stack.
46 lines
1023 B
JavaScript
46 lines
1023 B
JavaScript
/**
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* Copyright (c) 2013-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
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*/
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import invariant from 'fbjs/lib/invariant';
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/**
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* Accumulates items that must not be null or undefined.
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*
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* This is used to conserve memory by avoiding array allocations.
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*
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* @return {*|array<*>} An accumulation of items.
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*/
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function accumulate<T>(
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current: ?(T | Array<T>),
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next: T | Array<T>,
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): T | Array<T> {
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invariant(
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next != null,
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'accumulate(...): Accumulated items must be not be null or undefined.',
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);
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if (current == null) {
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return next;
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}
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// Both are not empty. Warning: Never call x.concat(y) when you are not
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// certain that x is an Array (x could be a string with concat method).
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if (Array.isArray(current)) {
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return current.concat(next);
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}
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if (Array.isArray(next)) {
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return [current].concat(next);
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}
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return [current, next];
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}
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export default accumulate;
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