JSON text is not a subset of PrimaryExpression

Mark S. Miller erights at google.com
Wed Jul 19 04:36:07 UTC 2017

I argued for that in the old es3.1 days. IIRC so did Mike Samuel and Crock.
The pain of doing it now would be higher than it would have been then.
Nevertheless, I would still be in favor.

Please draft a proposal. Thanks.

On Jul 18, 2017 8:16 PM, "Richard Gibson" <richard.gibson at gmail.com> wrote:

Another relevant option: Feature Request: Make ECMA262 a superset of JSON

On Tue, Jul 11, 2017 at 9:33 AM, Mike Samuel <mikesamuel at gmail.com> wrote:

> https://tc39.github.io/ecma262/#sec-json.parse says
> """
> Valid JSON text is a subset of the ECMAScript PrimaryExpression syntax
> as modified by Step 4 above. Step 2 verifies that JText conforms to
> that subset, and step 6 verifies that that parsing and evaluation
> returns a value of an appropriate type.
> """
> IIUC, if JSON text where a subset of PrimaryExpression then there
> should be no string that parses via JSON.parse which does not eval
> when wrapped in parentheses.
> On recent (Chrome, Safari, Firefox),
>     var s = String.fromCharCode(0x22, 0x2028, 0x22)
>     JSON.parse(s);   // Passes
>     eval('(' + s + ')');  // raises SyntaxError
> I believe the only reason it's not a subset is that both exclude line
> terminators from quoted string bodies but JSON does not treat U+2028
> and U+2029 as line terminator chars while EcmaScript does.
> Could we change "is a subset of" to "is almost a subset of" or "is a
> subset (modulo LineTerminators) of"?
> Some related discussion at
> https://esdiscuss.org/topic/json-response-to-statement-from-w3c-tag
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