NodeJS's __filename/__dirname in ES6 Modules

Gil Tayar gil at tayar.org
Sat Jan 21 18:10:08 UTC 2017


Andrea,

While it is true that "filename/URL" and "dirname" are not really important
in the browser world, they are used a lot in the Node world to read various
resources that reside in the same directory (or near the same directory) as
the module.

On Sat, Jan 21, 2017 at 7:49 PM Andrea Giammarchi <
andrea.giammarchi at gmail.com> wrote:

> FWIW I have both `__filename` and `__dirname` implemented in common-js
> package runtime, and these are resolved as absolute path from the root,
> unless imported externally where these are resolved as absolute URLs.
>
> Although I must say beside providing some debuggable information, without
> a core path module I don't see much added value in having these two
> references.
>
> I still load relatively via `module.import('./lib')` or
> `module.import('../js/file')`
>
> Regards
>
>
>
> On Sat, Jan 21, 2017 at 5:02 PM, Bradley Meck <bradley.meck at gmail.com>
> wrote:
>
> Please see
> https://github.com/tc39/proposal-dynamic-import#an-actual-function
>
> As per `"currentDir()" and "currentFile()"` this may not make sense for
> all URLs. Please use https://url.spec.whatwg.org/ which ships in Node v7+
> under `require('url').URL` and the proposal to bring it into the language
> itself https://github.com/jasnell/proposal-url . Getting the "directory"
> of a URL would be ~= `new URL('.', file_url)`.
>
> On Sat, Jan 21, 2017 at 10:42 AM, Gil Tayar <gil at tayar.org> wrote:
>
> Thanks!
>
> Makes total sense. So why not have Domenic's "import" be a real function
> that comes from this "js:context", thus obviating the need for a new
> JavaScript operator?
>
> While I realize that "js:context" will a Node thing, we could have a
> special import (e.g. import {...} from "js:system") that enables the system
> to expose real functions, of which one is "dynamicImport" and others would
> be "currentDir()" and "currentFile()".
>
> In other words - Domenic exposed a real need, but it seems that this need
> is more general, and not specific only to dynamic import, and should be
> added to the spec as a special import, just like it may be in Node.
>
>
> On Fri, Jan 20, 2017 at 6:48 PM Bradley Meck <bradley.meck at gmail.com>
> wrote:
>
> The current trend is towards the
> https://github.com/nodejs/node-eps/pull/39 rewrite which does not have
> magic variables
> https://github.com/bmeck/node-eps/blob/b14276ca093fac9cbc3b72ff5433df35ae67fb59/002-es-modules.md#341-environment-variables
>
> There are ideas about exposing the URL of the current ESM via something
> like
> https://docs.google.com/presentation/d/1aq_QjBUQTovj9aQZQrVzS7l1aiOs3ZNlk7wgNTUEMy0/edit#slide=id.g16ab11d101_0_22
>
> On Fri, Jan 20, 2017 at 10:42 AM, Gil Tayar <gil at tayar.org> wrote:
>
> While reading Dominic Denicola's spec for dynamic import() at
> https://github.com/tc39/proposal-dynamic-import, I read his rational for
> not having import be a regular function, but rather a "syntactic form". The
> idea is that import() needs to be "in the scope" of the current module, as
> it needs to resolve the module path it is given relative to the current
> module's.
> Thinking about it some more, I thought it would be a pity for import to be
> so "special", and asked myself whether there will be more features that
> will need to be "module-aware" like import().
>
> And there are! (I think...) - __filename and __dirname in NodeJS are
> exactly such features. Actually, anything passed to the function wrapping
> each NodeJS module is such a feature, but going over them, only __filename
> and __dirname are not immediately related to the module mechanism.
>
> So my question is this (and it is specifically addressed to the NodeJS
> implementors in the group): in NodeJS's implementation of ES6 modules, how
> will __dirname and __filename be implemented? Will there still be a
> function wrapper like in the current module implementation? Or will
> __dirname and __filename be a "syntactic form" like import()? Or something
> else?
>
> Thanks,
> Gil Tayar
>
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