Support JavaScript functions as arguments to Go calls

[cwc]

Reference: http://izs.me/v8-docs/classv8_1_1Function.html

JavaScript functions passed to Go appear to be nil values. I'm not sure what the ideal way would be to wrap the functions, but perhaps you'd have something like a V8Function object, with a Call(...args interface{}) method. Then Go could receive pointers to JavaScript functions and call back into them.

[cwc]

As mentioned in comments of #10, Call should be improved so that it accepts native Go types. Marshalling the args to JSON inside of Call will probably do the trick.

[mattn]

Probably, the code I just added will works well.

[mattn]

    v8ctx.AddFunc("func_call", func(args ...interface{}) interface{} {
        f := func(args ...interface{}) interface{} {
            return "V8"
        }
        ret, _ := args[0].(v8.V8Function).Call("Go", 2, 1, f)
        return ret
    })

    fmt.Println(v8ctx.MustEval(`
    func_call(function() {
        return "Hello " + arguments[0] + (arguments[1] - arguments[2])
            + ", Hello " + arguments[3]();
    })
    `).(string))

[cwc]

So the problem I'm running into now with Gonk is that if a function is passed through to Go as a callback that references variables in a local scope, those variables will not be visible when the callback is called from Go.

Example: https://github.com/Gonk/Gonk/blob/master/modules/pugme.js#L5-L7

When the callback function(err, res, body) is triggered from Go, it attempts to access the msg object. But since the function is just being evaled as a string, msg is undefined.

It would seem the only way to solve this is to somehow give Go V8Function objects a pointer to the original function in the V8 Context, and when Call() is used, call that function directly.

[mattn]

Hmm, It maybe must store V8Context in the scope.
Can you please show me a code reproduceable this issue?

[cwc]

I just fixed the unit tests; now I'll attempt to add a test case that demonstrates the issue.

[mattn]

Just added code to separate boolean/number/string.

[mattn]

Could you please try this in latest?

[mattn]

Added in 0ff6d39