Maintain the property characteristics (writable, configurable) following the execution of JSON.parse()

Question

Maintain the property characteristics (writable, configurable) following the execution of JSON.parse()

Imagine a scenario where an object is created elsewhere and passed to my module. It could have been generated on the server in node.js, or perhaps in a different module where it was then serialized using JSON.stringify() for transmission (especially if it originated from the server). I need to ensure that a specific property of this object remains immutable:

var foo = {};

Object.defineProperty(foo, 'bar', {
    value: 'bar',
    writeable: false,
    enumerable: true
});

console.log(foo.bar); //bar
foo.bar = 'foo';      //fails, throws err in strict
console.log(foo.bar); //still bar

var fii = JSON.parse(JSON.stringify(foo));

console.log(fii.bar); //still bar
fii.bar = 'foo';      //succeeds      
console.log(fii.bar); //now foo

Is there a way to preserve this metadata to ensure the immutability of the bar property without sending it separately?

javascript json

Answer 1

Answer №1

To serialize the property descriptors, you can convert them to strings like this:

// Define an object for serialization purposes, based on the initial question
var obj = {};
Object.defineProperty(obj, 'prop', {
    value: 'value',
    writable: true,
    enumerable: false
});

// Create an object to store property descriptors
var descriptors = {};
Object.keys(obj).forEach(function(key) {
    descriptors[key] = Object.getOwnPropertyDescriptor(obj, key);
});

var serialized = JSON.stringify(descriptors);
// "{"prop":{"value":"value","writable":true,"enumerable":false,"configurable":false}}"

Now, to deserialize:

descriptors = JSON.parse(serialized);
obj = {};
Object.defineProperties(obj, descriptors);

Keep in mind that this approach may not handle accessor-type descriptors, nested objects, etc.

Using flags within keys

Another technique is to include writability in the key names by applying transformations during serialization and deserialization:

// Indicate non-writable properties by adding ':unwritable' to the key name.
function flagImmutable(object) {
    for (var key in object) {
        if (!Object.getOwnPropertyDescriptor(object, key).writable) {
            object[key + ':unwritable'] = object[key];
            delete object[key];
        }
    }
}
flagImmutable(obj)
> Object {prop:unwritable: "value"}

After stringifying, apply the reverse transformation upon parsing.

Answer 2

To serialize the property descriptors, you can convert them to strings like this:

// Define an object for serialization purposes, based on the initial question
var obj = {};
Object.defineProperty(obj, 'prop', {
    value: 'value',
    writable: true,
    enumerable: false
});

// Create an object to store property descriptors
var descriptors = {};
Object.keys(obj).forEach(function(key) {
    descriptors[key] = Object.getOwnPropertyDescriptor(obj, key);
});

var serialized = JSON.stringify(descriptors);
// "{"prop":{"value":"value","writable":true,"enumerable":false,"configurable":false}}"

Now, to deserialize:

descriptors = JSON.parse(serialized);
obj = {};
Object.defineProperties(obj, descriptors);

Keep in mind that this approach may not handle accessor-type descriptors, nested objects, etc.

Using flags within keys

Another technique is to include writability in the key names by applying transformations during serialization and deserialization:

// Indicate non-writable properties by adding ':unwritable' to the key name.
function flagImmutable(object) {
    for (var key in object) {
        if (!Object.getOwnPropertyDescriptor(object, key).writable) {
            object[key + ':unwritable'] = object[key];
            delete object[key];
        }
    }
}
flagImmutable(obj)
> Object {prop:unwritable: "value"}

After stringifying, apply the reverse transformation upon parsing.

Maintain the property characteristics (writable, configurable) following the execution of JSON.parse()

Answer №1

Using flags within keys

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