url: set toStringTag for the URL class

[jasnell]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

url

Description

Add Symbol.toStringTag for URL class

Fixes: #10554

[targos]

Can you add a test?
And perhaps we should do the same to URLSearchParams?

[addaleax]

Wouldn’t it be a bit more customary to define this on the prototype?

[targos]

Web IDL requires that. The class string of the prototype should be URLPrototype.

[addaleax]

@targos Thanks for clarifying!

[benjamingr]

Can't it still be defined on the prototype and just make that decision as a getter when invoked? I'm not sure it's great to add another property on every URL object just for this?

[jasnell]

Yeah, I'd considered doing that but just went with the style already implemented for the other uses of toStringTag already in the file. We should update all of them if we're going to switch

[benjamingr]

If there is no performance regression then I'm not against merging this - otherwise we should probably update them with a prototype getter.

[TimothyGu]

The IDL spec says

If an object has a class string, then the object must, at the time it is created, have a property whose name is the @@toStringTag symbol and whose value is the specified string.

It specifically asked for the value of the property to be the class string (URL or URLSearchParams), which was why I used this form for URLSearchParams in the first place.

[benjamingr]

@TimothyGu that would still work when defining a getter on the prototype but without causing an extra slot allocation for every single URL/URLSearchParams object.

This is not that big of a deal, but a user might have hundreds of thousands of URL objects at once and not allocating the extra memory would be nice.

[jasnell]

PR has been updated to add a test and to move to using the getter on the class. The behavior now matches what is currently implemented by Firefox. Specifically:

const u = new url.URL('http://example.org');
const toString = Object.prototype.toString;
assert.strictEqual(toString.call(u), '[object URL]');
assert.strictEqual(Object.getPrototypeOf(u), '[object URLPrototype]');

const sp = u.searchParams;
assert.strictEqual(toString.call(sp), '[object URLSearchParams]');
assert.strictEqual(toString.call(Object.getPrototypeOf(sp)), '[object URLSearchParamsPrototype]');

Note that Chrome returns [object URL] for the getPrototypeOf check above.

[jasnell]

CI: https://ci.nodejs.org/job/node-test-pull-request/5691/

[jasnell]

AIX failure is unrelated

[jasnell]

Landed in f5d92f3