C++ API getOwnPropertyNames?

Here's what I'm trying to do:

Given an JSObject, can I get the names of its properties?

Extra credit -- this is with an obsolete version of Spidermonkey (1.8.5)

Use case: Inside a JSNative function we look for properties in an 
optional argument.

EG a JS_Native function takes one string argument, and an optional property:

var X = FindSomething_JSNative("a", { "look_really_hard" });

If none of the expected properties are defined, I want to print an error 
message giving the name of the unrecognized properties.