doc: res.getHeaders return value wrong in docs

[refack]

• Version: 7
• Platform: *
• Subsystem: HTTP

Ref: https://github.com/nodejs/node/pull/12883/files#r115149721

 const headersCopy = res.getHeaders();
 assert.ok(headersCopy instanceof Object);

Fails with AssertionError [ERR_ASSERTION]: false == true
In contradiction to API https://nodejs.org/api/http.html#http_response_getheaders

[refack]

More concretely
headersCopy.hasOwnProperty === undefined
&
headersCopy.propertyIsEnumerable === undefined

[addaleax]

See #12883 (comment) – can please you be precise about what the issue is or what you want to do here? Otherwise this issue is just stating facts.

[refack]

If there is a reason why it has a null prototype, we need to correct the API documentation.
Else just give it a prototype.

[addaleax]

If there is a reason why it has a null prototype

Yes, because header names can clash with the built-in fields of Object.prototype (for example with __proto__ itself).

correct the API

Are you talking about docs?

[refack]

Are you talking about docs?

Yes

[mscdex]

You can probably just copy the text from querystring.parse().