Why properties of an XMLHttpRequest object are only printable through console.log()?

Question

var obj = new XMLHttpRequest();
console.log("Object.keys():",Object.keys(obj));
console.log("Object.getOwnPropertyNames():",Object.getOwnPropertyNames(obj))
console.log("Object.entries():",Object.entries(obj))
console.log("JSON.stringify():",JSON.stringify(obj))

console.log("console.log:"); console.log(obj)

output:

Object.keys(): []
Object.getOwnPropertyNames(): []
Object.entries(): []
JSON.stringify(): {}
console.log:
XMLHttpRequest {onreadystatechange: null, readyState: 0, timeout: 0, withCredentials: false, upload: XMLHttpRequestUpload, …}

How can I create such an object in javascript, whose properties are only printed using console.log(obj), but not returned by any of the above functions?

I have already tried to create objects using constructor function, object.create() (with enumerable:false), Object.assign(), using getters, instatiating from a class, instatiating from an extended class e.t.c

Answer 1

How can I create such an object in javascript, whose properties are only printed using console.log(obj), but not returned by any of the above functions?

One close solution I have found is the one below. This will print properties with console.log(obj). However obj is a Proxy.

On chrome console the result is the same as XMLHttpRequest output (with class being Proxy). On firefox console it a representation of the Proxy class, so it is not exactly the same.

    const obj = new Proxy({prop1:"value1", prop2: "value2"}, {ownKeys: _=>[]});

    console.log("Object.keys():",Object.keys(obj));
    console.log("Object.getOwnPropertyNames():",Object.getOwnPropertyNames(obj))
    console.log("Object.entries():",Object.entries(obj))
    console.log("JSON.stringify():",JSON.stringify(obj))
    console.log(obj)

result:

Object.keys(): []
Object.getOwnPropertyNames(): []
Object.entries(): []
JSON.stringify(): {}
console.log:
Proxy {prop1: "value1", prop2: "value2"}

and console.log(obj.prop1) / obj.prop1="newValue" still works.