testconv.cpp

// compile me with:
// g++ -g -O0 -o testconv testconv.cpp `pkg-config --cflags --libs mozjs-24` -std=c++11
// output:
// JS_ValueToInt32: did not convert
// JS::ToInt32: converted, value is 0

#include <iostream>
#include <jsapi.h>

static JSClass global_class = {
    "global", JSCLASS_GLOBAL_FLAGS,
    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub,
    JS_StrictPropertyStub, JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
};

static void
define_element(JSContext *cx, JS::HandleObject array_obj, const char *text)
{
    JS::RootedString message(cx, JS_NewStringCopyZ(cx, text));
    JS::RootedValue val(cx, JS::StringValue(message));
    JS_DefineElement(cx, array_obj, 0, val, nullptr, nullptr, 0);
}

static void
print_results(const char *routine, bool worked, int32_t intval)
{
    std::cout << routine << ": ";
    if (worked)
        std::cout << "converted, value is " << intval;
    else
        std::cout << "did not convert";
    std::cout << std::endl;
}

int
main(void)
{
    JSRuntime *rt = JS_NewRuntime(8L * 1024 * 1024, JS_USE_HELPER_THREADS);
    if (!rt) return 1;
    JSContext *cx = JS_NewContext(rt, 8192);
    if (!cx) return 1;

    {
        JSAutoRequest ar(cx);
        JS::RootedObject global(cx,
            JS_NewGlobalObject(cx, &global_class, nullptr));
        if (!global) return 1;

        {
            JSAutoCompartment ac(cx, global);
            if (!JS_InitStandardClasses(cx, global)) return 1;

            JS::RootedObject array_obj(cx, JS_NewArrayObject(cx, 0, nullptr));
            define_element(cx, array_obj, "this");
            define_element(cx, array_obj, "is");
            define_element(cx, array_obj, "fine");
            JS::RootedValue array(cx, JS::ObjectValue(*array_obj));

            int32_t intval;
            bool worked = JS_ValueToInt32(cx, array, &intval);
            print_results("JS_ValueToInt32", worked, intval);

            worked = JS::ToInt32(cx, array, &intval);
            print_results("JS::ToInt32", worked, intval);
        }
    }

    JS_DestroyContext(cx);
    JS_DestroyRuntime(rt);
    return 0;
}