Template literal property names in object literals

Jordan Harband ljharb at gmail.com
Thu Nov 7 20:43:55 UTC 2019


It would create the ambiguity that "every property name not in brackets is
static/hardcoded" is no longer true.

On Thu, Nov 7, 2019 at 12:14 PM Alex Kodat <akodat at rocketsoftware.com>
wrote:

> Jordan,
>
> The sentiments in that link discuss the wisdom of having the StringLiteral
> definition include NoSubstitutionTemplate, a question about which I am
> agnostic, and wouldn't provide the full functionality I'm asking about,
> anyway.
>
> And I also understand that the spec currently only allows computed
> property names in square brackets.
>
> My suggestion was that ComputedPropertyName *could* be changed to include
> TemplateString (without square brackets). Whether this is worth doing or
> paints JS syntax into a corner is a fair question, but I don't see that
> adding TemplateString to ComputedPropertyName would create any syntactic
> ambiguities and wouldn't seem to present daunting implementation issues.
> But maybe this last assertion is incorrect and ambiguities would arise or
> implementation would be a nightmare?
>
> Thanks
>
> ------
> Alex Kodat
> Senior Product Architect
> Rocket Software
> t: +1 781 684 2294 • m: +1 315 527 4764 • w:
> http://www.rocketsoftware.com/
>
> From: Jordan Harband <ljharb at gmail.com>
> Sent: Thursday, November 7, 2019 1:46 PM
> To: Alex Kodat <akodat at rocketsoftware.com>
> Cc: Gus Caplan <me at gus.host>; es-discuss at mozilla.org
> Subject: Re: Template literal propery names in object literals
>
> Anything dynamic - computed - should be in brackets, since that's what
> that indicates.
>
> Thus, template literals with substitutions must require brackets.
>
> Based on sentiments like
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fecma262%2Fissues%2F1399%23issuecomment-452910799&data=02%7C01%7C%7Ca6f02ff84bd446c7593708d763bb3255%7C79544c1eed224879a082b67a9a672aae%7C0%7C0%7C637087527965990546&sdata=71bc85j8UPdAdkFjmprrximGsaySHt1o3r8zkV9ZYgQ%3D&reserved=0,
> either all template literals or none should be permitted in a given
> position.
>
> Thus, no change is possible.
>
> On Thu, Nov 7, 2019 at 10:00 AM Alex Kodat <mailto:
> akodat at rocketsoftware.com> wrote:
> Thanks Gus,
>
> Good stuff. Though I think I’d take a different tack on the discussion at
> that link, especially as I think the template literals should allow
> substitutions (why not?):
>
> let obj = { `${Date()}`: 1};
>
> I guess the tack I would take in the spec would be to add TemplateLiteral
> to ComputedPropertyName and not worry about whether or not it's a
> NoSubstitutionTemplate.
>
> Thanks
>
> ------
> Alex Kodat
> Senior Product Architect
> Rocket Software
> t: +1 781 684 2294 • m: +1 315 527 4764 • w:
> https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.rocketsoftware.com%2F&data=02%7C01%7C%7Ca6f02ff84bd446c7593708d763bb3255%7C79544c1eed224879a082b67a9a672aae%7C0%7C0%7C637087527965990546&sdata=d62CHuayKkj8EhttWHK9kbMjnnkMGJgrrDbZRjtlul0%3D&reserved=0
>
> From: Gus Caplan <mailto:me at gus.host>
> Sent: Thursday, November 7, 2019 11:13 AM
> To: Alex Kodat <mailto:akodat at rocketsoftware.com>
> Cc: mailto:es-discuss at mozilla.org
> Subject: Re: Template literal propery names in object literals
>
> Related discussion
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftc39%2Fecma262%2Fissues%2F1399&data=02%7C01%7C%7Ca6f02ff84bd446c7593708d763bb3255%7C79544c1eed224879a082b67a9a672aae%7C0%7C0%7C637087527965990546&sdata=8XRONc3vM6asxLzdeGYYKXaqkQ0ltiNzDgBD9en3X7s%3D&reserved=0
>
> On Thu, Nov 7, 2019 at 8:46 AM Alex Kodat <mailto:mailto:
> akodat at rocketsoftware.com> wrote:
> Just curious. Is there a reason template literals are not allowed as
> property names in object literals? I can do:
>
>    let obj = {'foo bar': 1};
>
> and
>
>    let obj = {"foo bar": 1};
>
> but not
>
>    let obj = {`foo bar`: 1};
>
> It doesn't seem that allowing the latter would present any syntactic
> problems and seems like almost an oversight that it's not allowed.
>
> The main reason I ask is that we've gone completely over to using template
> literals for all our literals (why not?) and was surprised that we can't
> use a template literal as an object literal property name. Obviously, we
> can do:
>
>    let obj = {[`foo bar`]: 1};
>
> And given that square brackets allow arbitrary expressions for propery
> names, it wouldn't seem that supporting template literals for object
> literal property names would not present any daunting implementation issues.
>
> I guess I'd argue that the Principle of Least Astonishment and/or
> completeness suggests that JS should support this.
>
> Sorry if this has been asked before but couldn't find anything in the
> archive.
>
> Thanks
>
> ------
> Alex Kodat
> Senior Product Architect
> Rocket Software
> t: +1 781 684 2294 • m: +1 315 527 4764 • w:
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