Intent to ship: JSON ⊂ ECMAScript

[Mathias Bynens]

Contact emails

mat...@chromium.org

Spec

https://github.com/tc39/proposal-json-superset

Summary

A Stage 3 proposal makes ECMAScript a syntactic superset of JSON by allowing U+2028 and U+2029 in string literals.

Motivation

ECMAScript claims JSON as a subset in JSON.parse, but (as has been well-documented) that is not true because JSON strings can contain unescaped U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR characters while ECMAScript strings cannot.

These exceptions add unnecessary complexity to the specification and increase the cognitive burden on both implementers and users, allowing for the introduction of subtle bugs. Also, as a lesser but concrete corollary problem, certain source concatenation and construction tasks currently require additional steps to process valid JSON into valid ECMAScript before embedding it.

Interoperability risk

Firefox: Public support

Edge: Public support

Safari: Public support

Web developers: Strongly positive

Compatibility risk

This change is backwards-compatible. User-visible effects will be limited to the elimination of SyntaxError completions when parsing strings that include unescaped LINE SEPARATOR or PARAGRAPH SEPARATOR characters, which in practice are uncommon.

Is this feature fully tested?

Yes; see v8/test/cctest/test-parsing/LineOrParagraphSeparator{AsLineTerminator,InStringLiteral,InStringLiteralHarmony}.

Tracking bug

https://bugs.chromium.org/p/v8/issues/detail?id=7418

Link to entry on the Chrome Platform Status dashboard

https://www.chromestatus.com/features/6102319234023424

Requesting approval to ship?

Yes

[PhistucK]

(At least on blink-dev)

"Interoperability risk" should have links for citing each vendor and web developer support.

☆PhistucK

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[Mathias Bynens]

Note that since this is a V8/JS feature, this post is just an FYI to blink-dev — no signoff from Blink API owners is required.

For ECMAScript features like this one, if a browser vendor would be opposed to this proposal, they would block its advancement at TC39. Given that this proposal already made it to Stage 3 I would be surprised if vendors would suddenly change their mind now.

[PhistucK]

I know.

Regarding "public support" - not "opposed" does not necessarily mean "support" (it could be neutral). Transparency is important in chromestatus.com (and in intent, I would argue).

Second, web developers are not part of the TC39 stages, so support or reactions from them are not a given (not as far as "strongly positive").

I think it makes sense to add links for opinions that are not your own.

Just my two or three cents.

☆PhistucK

[Sathya Gunasekaran]

LGTM

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[Benedikt Meurer]

LGTM!

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[Mathias Bynens]

For future reference: this landed in V8 v6.6.257 and should thus be available in Chrome 66.

LGTM!

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