Question

I am writing a C++ module for Node.js that wraps a C library, so we can use the C library from JavaScript. One of the functions in the C library takes an enum parameter, with the enum values included in the corresponding header file. I would like to export the enum values as integers from the C++ module so the Node.js application wouldn’t have to hardcode the value. Here is the basic idea:

C:

typedef enum 
{
    LOGLEVEL_ERROR = 0,
    LOGLEVEL_WARN,
    LOGLEVEL_INFO
} log_level_t;

write_to_log(log_level_t level, char* message);

C++:

Logger::Write(int level, char* message)
{
    write_to_log(level, message);
}

Node.js:

// This is what I want:
logger.write(logger.ERROR, "Oh no!  Something bad happened.");

How do I expose LOGLEVEL_ERROR from C++ so I can use logger.ERROR in JS? (I would even be OK with logger.LOGLEVEL_ERROR in JS.) I found an old Node.js native module that used a macro EXPORT_INT32 but this doesn’t seem to exist anymore (I’m using Node.js 0.8.8).

Answer 1

This is what I ended up doing:

Local<Object> instance = constructor->NewInstance(2, argv);

Local<Object> logLevel = Object::New();
logLevel->Set(String::NewSymbol("ERROR"), cvv8::CastToJS(LOGLEVEL_ERROR), ReadOnly);
logLevel->Set(String::NewSymbol("WARN"), cvv8::CastToJS(LOGLEVEL_WARN), ReadOnly);
logLevel->Set(String::NewSymbol("INFO"), cvv8::CastToJS(LOGLEVEL_INFO), ReadOnly);

instance->Set(String::NewSymbol("Level"), logLevel, ReadOnly);

Then from JavaScript you can access logger.Level.ERROR.