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

This has to do with the WhatWG console.log specification:

How the implementation prints args is up to the implementation, but implementations should separate the objects by a space or something similar, as that has become a developer expectation.

The spec leaves the output format very vague and it's up to the implementation to decide what to print.