Native Node.JS module - parsing an int[] from arguments - c++

Question

I am trying to write a native C++ module to include in a Node.js project -- I followed the guide here and have things setup pretty well.
The general idea is that I want to pass an array of integers to my C++ module to be sorted; the module then returns the sorted array.
However, I cannot compile using node-gyp build because I hit the following error:
error: no viable conversion from 'Local' to 'int *'
It is complaining about this code in my C++:
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
int* inputArray = args[0]; // <-- ERROR!
sort(inputArray, 0, sizeof(inputArray) - 1);
args.GetReturnValue().Set(inputArray);
}
This all makes conceptual sense to me -- the compiler can't magically cast arg[0] (presumably of type v8::Local) to an int*. Having said that, I cannot seem to find any way to get my argument successfully cast into a C++ integer array.
It should be known that my C++ is rather rusty, and I know next-to-nothing about V8. Can anyone point me in the right direction?

Answer 1

It's not trivial: you first need to unpack the JS array (internally represented as a v8::Array) into something sortable (like a std::vector), sort it, and convert it back to a JS array.
Here's an example:
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Make sure there is an argument.
if (args.Length() != 1) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Need an argument")));
return;
}
// Make sure it's an array.
if (! args[0]->IsArray()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "First argument needs to be an array")));
return;
}
// Unpack JS array into a std::vector
std::vector<int> values;
Local<Array> input = Local<Array>::Cast(args[0]);
unsigned int numValues = input->Length();
for (unsigned int i = 0; i < numValues; i++) {
values.push_back(input->Get(i)->NumberValue());
}
// Sort the vector.
std::sort(values.begin(), values.end());
// Create a new JS array from the vector.
Local<Array> result = Array::New(isolate);
for (unsigned int i = 0; i < numValues; i++ ) {
result->Set(i, Number::New(isolate, values[i]));
}
// Return it.
args.GetReturnValue().Set(result);
}
Disclaimer: I'm not a v8 wizard, nor a C++ one, so there may be better ways to do this.