console.log fails with const object = { __proto__: null }

[jsprog]

@c-smile Thanks for this link rollup/rollup#3140. I understand that they're sticking to the deprecated __proto__ for performance reasons to avoid changing object's prototype after it's creation (it's supported by browsers and some other runtimes including quickjs)

And according to this rollup/rollup#3096, __proto__: null is used to set the prototype of namespace objects to null.

quickjs has __proto__ according to these links:

• https://github.com/bellard/quickjs/blob/master/quickjs-atom.h
• https://www.freelists.org/post/quickjs-devel/JS-GetOwnPropertyNames-does-not-include--proto-,1

What I discovered:

• The Error only fires when using console.log(object_with__proto__null)
• The Error won't fire when using __proto__: undefined (not tested with browsers)
• You can access the object and assign it, but the moment you console.log the second reference, you'll receive the same error.
• You can console.log object's properties and Object.keys(object).
• The error has nothing to do with Object.freeze

Test Code:

const obj = {
    __proto__: null,
    a: 10,
    b: 20
};

obj; // Ok

obj.a = 11; // Ok
console.log('obj.a:', obj.a); // Ok: property changed to 11

Object.defineProperty(obj, 'a', { value: 12 });
console.log('obj.a:', obj.a); // Ok: property changed to 12

console.log('keys:', Object.keys(obj)); // Ok: not a problem at all

console.log('obj:', obj); // error
console.log(obj); // the same error
// error message:
// terminate called after throwing an instance of 'qjs::exception'
// Aborted (core dumped)

const obj_2 = obj; // Ok
console.log(obj_2); // The same error because it's refering to the same object

const obj_3 = { ...obj }; // Ok
console.log(obj_3); // Ok

[jsprog]

Unlike Chrome and Firefox, The current implementation of quickjs' console.log depends on the toString method. I already executed some tests under:

• The version provided by sciter.js (qjs)
• A Linux build (make) of the last version of quickjs (2020-11-08) https://bellard.org/quickjs/
• The online interactive version

Test under qjs (either the official version or the one that comes with sciter.js:

let obj = { prop1: 10, prop2: 20 }
console.log(Object.keys(obj)) // prop1,prop2
console.log(obj.toString()) // [object Object]
console.log(obj) // [object object]

obj = { __proto__: null, prop1: 30, prop2: 40 }
console.log(Object.keys(obj)) // prop1,prop2
console.log(obj.toString()) // TypeError: not a function
                            // at <eval> (./log_obj_with__proto__null.js:8)
console.log(obj) // TypeError: toPrimitive
                 //     at log (native)
                 //     at <eval> (./log_obj_with__proto__null.js:10)

The same test at https://bellard.org/jslinux/vm.html?url=alpine-x86.cfg:

Note: I'm not in a position to decide behalf others if console.log should behave differently from the current implementation. I can still write something like console.log({...obj}) or even get rid of __proto__:null whenever needed. Let's hear what others have to say about this.

[4silvertooth]

Why is it so important to console.log an object with __proto__ :null, I mean I feel you have invested a lot time on it. What's the importance?

[c-smile]

For now console.log is just a placeholder. It is there for initial development.
In different environments console.log and console in general mean different things.
For real app console.log is just a file.write() or something like that.
For app running with inspector console.log will be redefined as inpector.pipe.write and so on.

In any case it can be redefined on script side:

console,log = function(args...) {  }

with proper checks for thing.toString existence.

[jsprog]

@4silvertooth

Why is it so important to console.log an object with proto :null,

I don't write __proto__ in my code. I console.log for inspection regardless whether the target contained a prototype or not. It was just a coincidence that rollup injected it. (note: console.log(JSON.stringify(object)) is tested to work)

I mean I feel you have invested a lot time on it. What's the importance?

• I'm the one who made the noise, I don't fire and forget, but I do something from my side, to later share back the results.
• I mind about the success of sciter.js to run some popular reactive frameworks.

@c-smile Feel free to close this anytime.

[c-smile]

Thanks a lot for digging it.

I am using toString() in other places so this finding will help there too.

[c-smile]

Fixed in 4.4.5.5