80 lines
2.3 KiB
JavaScript
80 lines
2.3 KiB
JavaScript
/**
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* Copyright (c) 2015-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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* @flow
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* @format
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* @providesModule asyncRequire
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*/
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'use strict';
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/**
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* The bundler must register the dependency properly when generating a call to
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* `asyncRequire`, that allows us to call `require` dynamically with confidence
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* the module ID is indeed valid and available.
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*/
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function asyncRequire(moduleID: number): Promise<mixed> {
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return Promise.resolve()
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.then(() => {
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const {segmentId} = (require: $FlowFixMe).unpackModuleId(moduleID);
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return loadSegment(segmentId);
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})
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.then(() => require.call(null, (moduleID: $FlowFixMe)));
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}
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let segmentLoaders = new Map();
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/**
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* Ensure that a bundle segment is ready for use, for example requiring some of
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* its module. We cache load promises so as to avoid calling `fetchSegment`
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* twice for the same bundle. We assume that once a segment is fetched/loaded,
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* it is never gettting removed during this instance of the JavaScript VM.
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*
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* Segment #0 is the main segment, that is always available by definition, so
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* we never try to load anything.
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*
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* We don't use async/await syntax to avoid depending on `regeneratorRuntime`.
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*/
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function loadSegment(segmentId: number): Promise<void> {
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return Promise.resolve().then(() => {
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if (segmentId === 0) {
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return;
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}
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let segmentLoader = segmentLoaders.get(segmentId);
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if (segmentLoader != null) {
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return segmentLoader;
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}
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const {fetchSegment} = global;
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if (fetchSegment == null) {
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throw new FetchSegmentNotAvailableError();
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}
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segmentLoader = new Promise((resolve, reject) => {
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fetchSegment(segmentId, error => {
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if (error != null) {
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reject(error);
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return;
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}
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resolve();
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});
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});
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segmentLoaders.set(segmentId, segmentLoader);
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return segmentLoader;
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});
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}
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class FetchSegmentNotAvailableError extends Error {
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constructor() {
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super(
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'When bundle splitting is enabled, the `global.fetchSegment` function ' +
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'must be provided to be able to load particular bundle segments.',
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);
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}
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}
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module.exports = asyncRequire;
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