react-native/Libraries/Utilities/deepFreezeAndThrowOnMutatio...

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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
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*
* @providesModule deepFreezeAndThrowOnMutationInDev
* @flow
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*/
'use strict';
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/**
* If your application is accepting different values for the same field over
* time and is doing a diff on them, you can either (1) create a copy or
* (2) ensure that those values are not mutated behind two passes.
* This function helps you with (2) by freezing the object and throwing if
* the user subsequently modifies the value.
*
* There are two caveats with this function:
* - If the call site is not in strict mode, it will only throw when
* mutating existing fields, adding a new one
* will unfortunately fail silently :(
* - If the object is already frozen or sealed, it will not continue the
* deep traversal and will leave leaf nodes unfrozen.
*
* Freezing the object and adding the throw mechanism is expensive and will
* only be used in DEV.
*/
function deepFreezeAndThrowOnMutationInDev(object: Object) {
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if (__DEV__) {
if (typeof object !== 'object' ||
object === null ||
Object.isFrozen(object) ||
Object.isSealed(object)) {
return;
}
for (var key in object) {
if (object.hasOwnProperty(key)) {
object.__defineGetter__(key, identity.bind(null, object[key]));
object.__defineSetter__(key, throwOnImmutableMutation.bind(null, key));
}
}
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Object.freeze(object);
Object.seal(object);
for (var key in object) {
if (object.hasOwnProperty(key)) {
deepFreezeAndThrowOnMutationInDev(object[key]);
}
}
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}
}
function throwOnImmutableMutation(key, value) {
throw Error(
'You attempted to set the key `' + key + '` with the value `' +
JSON.stringify(value) + '` on an object that is meant to be immutable ' +
'and has been frozen.'
);
}
function identity(value) {
return value;
}
module.exports = deepFreezeAndThrowOnMutationInDev;