Please help with writing spec for async JSON APIs

Allen Wirfs-Brock allen at
Mon Aug 3 17:29:33 UTC 2015

On Aug 3, 2015, at 9:02 AM, James M Snell wrote:

> On Mon, Aug 3, 2015 at 8:34 AM, Allen Wirfs-Brock <allen at> wrote:
> [snip]
>> 4) JSON.parse/stringify are pure computational  operations.  There is no
>> perf benefit to making them asynchronous unless some of their computation
>> can be performed concurrently.
> If we're speaking strictly about making the JSON parsing asynchronous,
> then correct, there is really no performance benefit to speak of. You
> may be able to offload the parsing to a separate thread, but it's
> going to take the same amount of time. The real benefit will come when
> (a) JSON parsing becomes incremental

yes, incremental is good.  But do you really mean just "parsing" rather than "processing"? 

> and (b) a developer is given
> greater control over exactly how the JSON is converted to/from
> strings.

Strictly speaking JSON is strings.  JSON.stringify/parse converts JS values (including objects) to/from such strings.

> Something along the lines of...
> JSON.parser(input).
>  on('key', function(key, context) {
>    if (key === 'foo')
>      console.log(context.value());
>    else if (key === 'bar')
>      context.on('key', ...);
>  }).
>  on('end', function() {
>  });

I have to guess at your semantics, but what you are trying to express above seems like something that can already be accomplished using the `reviver` argument to JSON.parse.

> In other words: allowing for incremental access to the stream and fine
> grained control over the parsing process, rather than having to block
> while everything is parsed out, building up the in-memory object
> model, then being forced to walk that model in order to do anything
> interesting.
> Personally, I'm not overly concerned about the possibility of races.

But, TC39 is concerned about races.

> - James

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