Implement a named property handler & a indexed property handler on the object about duktape

[svaarala]

The current mechanisms for property virtualization are: (1) plain setters/getters and (2) the E6 Proxy object. Both setters/getters and Proxy traps can be native Duktape/C functions.

For more concreteness, could you describe what use case you would like to solve which is not addressed by current mechanisms?

[hyunjunekim]

If use Proxy, Does a object which is proxy break the proto chain?

[hyunjunekim]

For example,
var person = {phone:"000-000"}
var student = {age:20}
student.proto = person;
var sam = Object.create(student);
sam.name // need point about named property.
This situation, Don't describe using Proxy.

[svaarala]

Hmm, just to be sure: sam inherits from student which inherits from person, and name is intended to represent a virtual property that doesn't exist in the target (sam)?

Anyway, Proxy will capture all property reads and the 'get' trap can freely decide to provide property values out of thin air or to read them from the target object. For instance, sam.name would invoke the 'get' trap, and you could return whatever you want for 'name' without having that property in the target object.

[hyunjunekim]

If sam Object turn Proxy, has a problem that sam object' proto is proxy.
I want that sam object's proto is student.

[svaarala]

Duktape's Proxy implementation is not yet complete - do you mean that there is an issue with Duktape's Proxy or the ES6 Proxy model in general?

When you say that it's a problem that sam object's proto is proxy, what breaks in practice? At least property reads and writes should go normally through the Proxy, so I'm not sure what concretely breaks in your code.

[hyunjunekim]

I mean we should support the general Object like V8.(http://izs.me/v8-docs/classv8_1_1ObjectTemplate.html)

[svaarala]

Unfortunately that doesn't really tell me what the concrete problem is that you cannot solve with Proxy. Duktape doesn't attempt to copy V8's API so it's not really a useful feature request to copy a V8 API without concrete motivation what we're trying to achieve.

[svaarala]

Just to get some concreteness, here's an example of using a Proxy to provide a virtual "name":

var person = { phone: "000-000" };
var student = { age: 20 }; Object.setPrototypeOf(student, person);
var samRaw = Object.create(student);
var sam = new Proxy(samRaw, {
    get: function (targ, key) {
        // Virtual properties
        if (key === 'name') {
            return 'fake name';  // whatever logic here
        }

        // Not a virtual property, continue lookup from target
        return targ[key];
    }
});

print('phone is:', sam.phone);
print('age is:', sam.age);
print('name is:', sam.name);

When executed with the Duktape command line, this prints:

phone is: 000-000
age is: 20
name is: fake name

Trapping property writes would be handled similarly with the set trap.

[hyunjunekim]

@svaarala Wow. I'm understand.
print(sam.proto == student) // result : true
Thank you.

[svaarala]

I'm happy if the Proxy solved your issue, but I'm not sure if it was a good solution or just an adequate solution :) There's certainly room for improvement for property / object virtualization so feel free to open an issue if you run into something that doesn't quite work :)

[hyunjunekim]

@svaarala If exist this API, I think very useful. So reopen this issue.
and Thank you for help. :)

[hyunjunekim]

@svaarala I have last question. Is it possible that wrap proxy in the global object?

[svaarala]

There's a Duktape/C API call to replace the global object with a new one:

• http://duktape.org/api.html#duk_set_global_object

Technically you should be able to give a Proxy object as the new global object.

[hyunjunekim]

@svaarala Is this API named "duk_set_global_object" since 0.11.0?

[svaarala]

The duk_set_global_object() call was added in 0.12.0.

[hyunjunekim]

@svaarala :) Thank you. 💯 Now, I'am happy. because of you.

[svaarala]

Glad to help, let me know if you run into further issues :)

[svaarala]

@hyunjunekim I'll close this issue: there's no concrete work item here as just copying a certain V8 feature "as is" is a bit too vague. If you run into concrete problems, you can open a separate issue for those.