import.meta.url, and import.meta generally

[domenic]

Dear Sirs and Madam of TAG!

Another ECMAScript/web platform-spanning review for you all.

• Name: import.meta, with specific focus on import.meta.url
• Specification URL:
  • JavaScript-side spec (import.meta in general): https://tc39.github.io/proposal-import-meta/
  • HTML-side spec (import.meta.url): Add import.meta.url whatwg/html#3141
• Explainer, Requirements Doc, or Example code:
  • https://github.com/tc39/proposal-import-meta/blob/master/README.md
  • May also be interesting: presentation that helped originate this feature
• Tests: [import.meta.url] Implement import.meta.url behind flag (Blink-side) web-platform-tests/wpt#7888
• Primary contacts: @domenic, @gsathya, @hiroshige-g

Further details (optional):

• Relevant time constraints or deadlines: we plan to ship this in Chrome 63, which branches in mid October and ships in early December
• I have read and filled out the Self-Review Questionnare on Security and Privacy. The assessment is no to all/no difference in incognito mode.
• I have reviewed the TAG's API Design Principles

You should also know that...

This design went through a lot of discussion at TC39 as to the exact syntax for exposing per-module metadata. You can find some minutes discussing the above-linked presentation if you are curious as to how the specific choices here were arrived at.

We'd prefer the TAG provide feedback as (please select one):

• open issues in our Github repo for each point of feedback
• open a single issue in our Github repo for the entire review
• leave review feedback as a comment in this issue

If the TAG is interested, we're currently trying to figure out how to add a second import.meta property, import.meta.scriptElement, but it is a bit tricky. Feel free to help us out at whatwg/html#1013; the trouble starts around whatwg/html#1013 (comment) .

[torgo]

We discussed on today's call. @slightlyoff to write some feedback.

[slightlyoff]

Wow, sorry for leaving this so long.

I note that this has probably shipped: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Hq3cVNto74c

In general, the feature looks hugely useful. My only concern is about naming collisions. Given that names are added by host environments, it would seem best if there were a central registry.

[annevk]

Per https://tc39.github.io/proposal-import-meta/ the host (of which there's always one) supplies all the values, so by definition whoever implements HostGetImportMetaProperties (HTML Standard in case of the web platform) will define the registry.

[lin7sh]

what about import.meta.scriptElement?

[slightlyoff]

@annevk: HTML having a unique registry (not shared, ala IANA) is exactly the problem I was trying to raise. Happy to see this ship, but would like to see the registry situation end up in a more centralized place across specs and stacks.

[annevk]

@slightlyoff fair, I raised tc39/proposal-import-meta#14 to see if some alternate design can be considered that encourages cross-host collaboration.