how to get the lexical scope of an executed script

lexical.cpp

/* g++ -g -Wno-invalid-offsetof -DDEBUG -std=c++11 -o lexical `pkg-config --cflags --libs mozjs-45` lexical.cpp */

#include <iostream>

#include "js-config.h"
#include "jsapi.h"
#include "js/Initialization.h"
#include "jsfriendapi.h"

static JSClass global_class = {
    "global", JSCLASS_GLOBAL_FLAGS,
    nullptr, nullptr, nullptr, nullptr, nullptr,
    nullptr, nullptr, nullptr, nullptr, nullptr,
    nullptr,
    JS_GlobalObjectTraceHook
};

static bool
import1(JSContext *cx, const char *script, JS::MutableHandleObject module,
    JS::MutableHandleObject lexical)
{
    module.set(JS_NewGlobalObject(cx, &global_class, nullptr,
                                  JS::FireOnNewGlobalHook));

    JSAutoCompartment ac(cx, module);
    JS::CompileOptions options(cx);
    options.setUTF8(true);

    JS::RootedValue dummy_retval(cx);
    if (!JS::Evaluate(cx, options, script, strlen(script), &dummy_retval))
        return false;

    lexical.set(JS_GlobalLexicalScope(module));
    return true;
}

static bool
import2(JSContext *cx, const char *script, JS::HandleObject global,
    JS::MutableHandleObject module, JS::MutableHandleObject lexical)
{
    JS::CompileOptions options(cx);
    options.setUTF8(true);

    JS::RootedScript compiled_script(cx);
    if (!JS::CompileForNonSyntacticScope(cx, options, script, strlen(script),
                                         &compiled_script))
        return false;

    /* This function says it should not be used */
    if (!js::ExecuteInGlobalAndReturnScope(cx, global, compiled_script, lexical))
        return false;

    JS::RootedValue non_syntactic_variables(cx, JS_GetReservedSlot(lexical, 0));
    module.set(&non_syntactic_variables.toObject());
    return true;
}

int main(int argc, const char *argv[])
{
    JS_Init();
    JSRuntime *rt = JS_NewRuntime(8L * 1024 * 1024);
    JSContext *cx = JS_NewContext(rt, 8192);

    {
        JSAutoRequest ar(cx);

        JS::RootedObject global(cx,
            JS_NewGlobalObject(cx, &global_class, nullptr, JS::FireOnNewGlobalHook));
        JSAutoCompartment ac(cx, global);

        JS_InitStandardClasses(cx, global);

        const char *script = "var a = 1; let b = 2; const c = 3;";
        JS::RootedObject module(cx), lexical(cx);

        std::cout << "---- Using ExecuteScript ----\n";

        if (!import1(cx, script, &module, &lexical))
            return 1;
        js::DumpObject(module);
        js::DumpObject(lexical);

        std::cout << "--- Using ExecuteInGlobalAndReturnScope ----\n";

        module = nullptr;
        lexical = nullptr;
        if (!import2(cx, script, global, &module, &lexical))
            return 1;
        js::DumpObject(module);
        js::DumpObject(lexical);
    }

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

output.txt

---- Using ExecuteScript ----
object 0x107b87060 from global 0x107b87060 [global]
class 0x1063682b0 global
flags: delegate varobj unqualified_varobj
proto null
reserved slots:
   0 (reserved) = undefined
...etc...
 154 (reserved) = undefined
 155 (reserved) = <Block object at 0x107b88070>
 156 (reserved) = undefined
...etc...
 178 (reserved) = undefined
properties:
    ((js::Shape*) 0x107b86128) enumerate permanent JSString* (0x107b00940) = Latin1Char * (0x107b00948) = "a"
: slot 179 = 1

object 0x107b88070 from global 0x107b87060 [global]
class 0x106cc0320 Block
flags: delegate
proto <Block object at 0x107b88040>
reserved slots:
   0 (reserved) = <global object at 0x107b87060>
   1 (reserved) = <global object at 0x107b87060>
properties:
    ((js::Shape*) 0x107b86150) enumerate permanent JSString* (0x107b00958) = Latin1Char * (0x107b00960) = "b"
: slot 2 = 2
    ((js::Shape*) 0x107b86178) enumerate readonly permanent JSString* (0x107b00970) = Latin1Char * (0x107b00978) = "c"
: slot 3 = 3

--- Using ExecuteInGlobalAndReturnScope ----
object 0x107b63190 from global 0x107b62060 [global]
class 0x106cc01f8 NonSyntacticVariablesObject
flags: delegate varobj unqualified_varobj
proto null
reserved slots:
   0 (reserved) = <Block object at 0x107b63070>
properties:
    ((js::Shape*) 0x107b83858) enumerate permanent JSString* (0x107b00940) = Latin1Char * (0x107b00948) = "a"
: slot 1 = 1

object 0x107b631f0 from global 0x107b62060 [global]
class 0x106cc0320 Block
flags: delegate
proto <Block object at 0x107b631c0>
reserved slots:
   0 (reserved) = <NonSyntacticVariablesObject object at 0x107b63190>
   1 (reserved) = <global object at 0x107b62060>
properties:
    ((js::Shape*) 0x107b83880) enumerate permanent JSString* (0x107b00958) = Latin1Char * (0x107b00960) = "b"
: slot 2 = 2
    ((js::Shape*) 0x107b838a8) enumerate readonly permanent JSString* (0x107b00970) = Latin1Char * (0x107b00978) = "c"
: slot 3 = 3