How to Implement Closures Using SpiderMonkey API?

Question

I've been working with the SpiderMonkey C API and would like to implement a closure in C using their API. The one I would like to implement is fairly complex, but I can't even figure out how to do a simple one such as:

function x() {
   var i = 0;
   return function() { i++; print(i); };

}

var y = x();
y(); //1
y(); //2
y(); //3

I was wondering if anyone knows how I might do this. I found the JS_NewFunction method, but I don't actually know if that is a step in the right direction. Any help will be appreciated, thanks!

Answer 1

I don't know if there's a pure C way of doing closures or not. I would reccomend though, if you can, to just implement the functionality you need in javascript, and simply evaluate the javascript text in JSAPI. From there, use JSAPI to grab whatever handles/variables you need to implement your host functionality. It's really onerous to do javascripty things using JSAPI, avoid it if you can.

Answer 2

Narrated as if you're probably still interested, a year later.

Knitting my brows furiously at the documentation for JS_GetParent, I see

For some functions, it is used to implement lexical scoping (but this is an implementation detail).

and then, along with a list of API functions that create functions,

Some of these functions allow the application to specify a parent object. If the JSAPI function creating the object has a parent parameter, and the application passes a non-null value to it, then that object becomes the new object's parent. Otherwise, if the context is running any scripts or functions, a default parent object is selected based on those.

I might experiment with this later, but it seems that you might be able to do this either by (merely) creating the function in the API during the execution of the function that you want it to have the scope of.

Otherwise, you might be able to set the lexical scope of a function to some object manually using JS_SetParent, but the documentation keeps ominously calling that use of parents 'internal'.

</necro>