Regarding `typeOf` examples

[brettz9]

A few different observations or suggestions regarding the typeOf examples:

1. new WebAssembly.Module() would I guess give the same as the Module exotic object:

   import * as util from './util.js';`
   Builtin.typeOf(util);

   ... so maybe the above should be indicated as such (if not differentiated)?

2. I think NaN and arguments are interesting enough to describe their expected values
3. I'd be curious to know whether it would be expected that host environments like browsers would end up making DOM objects return their name (e.g., HTMLSelectElement), and if so, maybe raising an example possibility would even better demonstrate the potential.

[ljharb]

2. NaN is a primitive; i think Number.isNaN is sufficient to detect that. arguments already has a ToStringTag, so there's no reason it wouldn't be able to report "Arguments" here.

3. yes, just like ToStringTag (which was primarily added for HTML elements, as I understand it), this would allow engines to do the same.

[brettz9]

Ah yes, re: arguments, thank you.

While NaN can be detected by Number.isNaN, it seems unnecessarily cumbersome (and making for less immediately readable code) to need to add a special type-checking case for it; moreover, I'd expect most uses of type-based switch statements would not be seeking to treat NaN the same as number (and if they were, they could easily add another fall-through case to handle both together).

[ljharb]

the type of NaN is number; it wouldn't be appropriate for something called "typeOf" to return anything other than "number" for it.

[brettz9]

The typeof of null is, and with this proposal, remains, "object" as well. There can be different types of types. :-)

[brettz9]

And looking at it semantically, "not a number" is not a number. :-)

[ljharb]

NaN represents “no number”, just like null represents “no object” ¯\_(ツ)_/¯

[brettz9]

Despite the spec naming it "Not-a-Number", I think that is a fair characterization. However, again, the proposal currently (and thankfully) distinguishes null from "object".

[ljharb]

Indeed; this is more akin to Object.prototype.toString.call(null).slice(8, -1) :-)