Is V8::JSON::Parse really needed against JSON inputs?

[Abhishek Singh]

Hi,

I'm trying to send JSON data to user supplied JS code, which is executed by V8. What I've realised is even if user data is JSON marshalled, I've to explicitly do V8::JSON::Parse on it, so that value received in JS world is native JS JSON. Is that really necessary? Performance penalty because of it, is quite high(screenshot of profile attached).

[Jakob Kummerow]

What do you mean by "native JS JSON"?

JSON ("JavaScript Object Notation") is a standardized format for string representations of objects. "JSON.stringify" creates this string representation for a given object, "JSON.parse" creates a new object from this string representation. If you want to transfer a string, and then create an object from it, then JSON.Parse (which is exposed as V8::JSON::Parse in the V8 API) is the way to go.

(Depending on your use case, instead of transferring a JSON string, passing around an ArrayBuffer with externalized data might be a better fit. Then there would be no conversions to string and back.)

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[Abhishek Singh]

Hi,

(responses inline)

On 16-Mar-2017, at 21:53, Jakob Kummerow <jkum...@chromium.org> wrote:

What do you mean by "native JS JSON"?

Apologies, it isn’t technically correct term. I meant javascript object carved out of string representation.

JSON ("JavaScript Object Notation") is a standardized format for string representations of objects. "JSON.stringify" creates this string representation for a given object, "JSON.parse" creates a new object from this string representation. If you want to transfer a string, and then create an object from it, then JSON.Parse (which is exposed as V8::JSON::Parse in the V8 API) is the way to go.

(Depending on your use case, instead of transferring a JSON string, passing around an ArrayBuffer with externalized data might be a better fit. Then there would be no conversions to string and back.)

For current use case, I need to operate on few top level fields of JS object(made out of stringified representation on already JSON marshalled data) - so I think ArrayBuffer might not work out. Sample ex:

function OnUpdate(doc, meta) {

    if (doc.type == “credit_score”) {

var res = CalculateCreditScore(doc)

    }

}

2 args passed to OnUpdate->Call() are already JSON marshalled(but present as string, so was hoping if I could avoid marshalling it twice). I suppose, I would have to stick JSON.parse to handle above kind of use case.

Is there a way to expose a custom encoded data(flatbuffer encoded probably, it’s cpu footprint looks good) to JS world and access fields from it - i.e. args passed to OnUpdate->Call() could be stringified flatbuffer encoded data and then somehow we could access fields in flatbuffer schema directly from JS?

On Thu, Mar 16, 2017 at 3:39 PM, Abhishek Singh <singhabh...@gmail.com> wrote:

Hi,

I'm trying to send JSON data to user supplied JS code, which is executed by V8. What I've realised is even if user data is JSON marshalled, I've to explicitly do V8::JSON::Parse on it, so that value received in JS world is native JS JSON. Is that really necessary? Performance penalty because of it, is quite high(screenshot of profile attached).

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[Jakob Kummerow]

Of course it's possible to make C++ objects accessible to JS, that's what V8's API is for. You'll have to provide accessors for fields you want to expose. See https://github.com/v8/v8/wiki/Embedder's-Guide#accessing-dynamic-variables.