mattermost-redux/src/utils/deep_freeze.ts

Common code (API client, Redux stores, logic, utility functions) for building a Mattermost client

/**
 * 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.
 *
 */

/* eslint-disable header/header */

/**
 * 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.
 */

export default function deepFreezeAndThrowOnMutation(object: any): any {
    // Some objects in IE11 don't have a hasOwnProperty method so don't even bother trying to freeze them

    if (typeof object !== 'object' || object === null || Object.isFrozen(object) || Object.isSealed(object)) {
        return object;
    }

    for (const key in object) {
        if (object.hasOwnProperty(key)) {
            object.__defineGetter__(key, identity.bind(null, object[key])); // eslint-disable-line no-underscore-dangle
            object.__defineSetter__(key, throwOnImmutableMutation.bind(null, key)); // eslint-disable-line no-underscore-dangle
        }
    }

    Object.freeze(object);
    Object.seal(object);

    for (const key in object) {
        if (object.hasOwnProperty(key)) {
            deepFreezeAndThrowOnMutation(object[key]);
        }
    }

    return object;
}

function throwOnImmutableMutation(key: string, value: any) {
    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: any): any {
    return value;
}