68 lines
1.9 KiB
JavaScript
68 lines
1.9 KiB
JavaScript
/**
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* Copyright (c) 2013-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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* @providesModule defineLazyObjectProperty
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* @flow
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*/
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'use strict';
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/**
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* Defines a lazily evaluated property on the supplied `object`.
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*/
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function defineLazyObjectProperty<T>(
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object: Object,
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name: string,
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descriptor: {
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get: () => T,
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enumerable?: boolean,
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writable?: boolean,
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},
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): void {
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const {get} = descriptor;
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const enumerable = descriptor.enumerable !== false;
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const writable = descriptor.writable !== false;
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let value;
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let valueSet = false;
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function getValue(): T {
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// WORKAROUND: A weird infinite loop occurs where calling `getValue` calls
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// `setValue` which calls `Object.defineProperty` which somehow triggers
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// `getValue` again. Adding `valueSet` breaks this loop.
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if (!valueSet) {
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// Calling `get()` here can trigger an infinite loop if it fails to
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// remove the getter on the property, which can happen when executing
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// JS in a V8 context. `valueSet = true` will break this loop, and
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// sets the value of the property to undefined, until the code in `get()`
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// finishes, at which point the property is set to the correct value.
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valueSet = true;
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setValue(get());
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}
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return value;
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}
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function setValue(newValue: T): void {
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value = newValue;
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valueSet = true;
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Object.defineProperty(object, name, {
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value: newValue,
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configurable: true,
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enumerable,
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writable,
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});
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}
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Object.defineProperty(object, name, {
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get: getValue,
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set: setValue,
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configurable: true,
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enumerable,
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});
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}
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module.exports = defineLazyObjectProperty;
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