Sepehr Sepehr - 4 months ago 27
Node.js Question

Make v8 object properties and methods visible to JS

I am wrapping a C++ object with

node::ObjectWrap
and I have some methods defined like:

auto tpl = NanNew<v8::FunctionTemplate>(New);
tpl->SetClassName(NanNew("className"));
tpl->InstanceTemplate()->SetInternalFieldCount(4);

NanSetPrototypeTemplate(tpl, NanNew("method1") , NanNew<v8::FunctionTemplate>(Method1) , v8::ReadOnly);
NanSetPrototypeTemplate(tpl, NanNew("method2") , NanNew<v8::FunctionTemplate>(Method2), v8::ReadOnly);
NanSetPrototypeTemplate(tpl, NanNew("method3") , NanNew<v8::FunctionTemplate>(Method3) , v8::ReadOnly);
NanSetPrototypeTemplate(tpl, NanNew("method4") , NanNew<v8::FunctionTemplate>(Method4), v8::ReadOnly);


Everything works just as expected and I can make an instance of the object in JS by:

var classInstance = new className();


All methods work just fine but when I try to log the function:

console.log(classInstance);


I am expecting to see something like:

{
method1 : [Native Function],
method2 : [Native Function],
method3 : [Native Function],
method4 : [Native Function]
}


But what I get is:

{}


Any thoughts on how to make these visible (aka enumerable)?

Answer

What you have is essentially

var tpl = function(){};
tpl.prototype.method1 = function(){};
tpl.prototype.method2 = function(){};
tpl.prototype.method3 = function(){};
tpl.prototype.method4 = function(){};

var inst = new tpl();

console.log(tpl);

The thing is that what is printed out does not include values in the prototype chain. So inst doesn't actually have any properties to print, hence {}. Only inst.__proto__ has properties. The properties are enumerable, so you could do Object.keys(inst.__proto__); to see them, but they aren't own properties of inst.