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callback.md
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## Nan::Callback
`Nan::Callback` makes it easier to use `v8::Function` handles as callbacks. A class that wraps a `v8::Function` handle, protecting it from garbage collection and making it particularly useful for storage and use across asynchronous execution.
- <a href="#api_nan_callback"><b><code>Nan::Callback</code></b></a>
<a name="api_nan_callback"></a>
### Nan::Callback
```c++
class Callback {
public:
Callback();
explicit Callback(const v8::Local<v8::Function> &fn);
~Callback();
bool operator==(const Callback &other) const;
bool operator!=(const Callback &other) const;
v8::Local<v8::Function> operator*() const;
MaybeLocal<v8::Value> operator()(AsyncResource* async_resource,
v8::Local<v8::Object> target,
int argc = 0,
v8::Local<v8::Value> argv[] = 0) const;
MaybeLocal<v8::Value> operator()(AsyncResource* async_resource,
int argc = 0,
v8::Local<v8::Value> argv[] = 0) const;
void SetFunction(const v8::Local<v8::Function> &fn);
v8::Local<v8::Function> GetFunction() const;
bool IsEmpty() const;
void Reset(const v8::Local<v8::Function> &fn);
void Reset();
MaybeLocal<v8::Value> Call(v8::Local<v8::Object> target,
int argc,
v8::Local<v8::Value> argv[],
AsyncResource* async_resource) const;
MaybeLocal<v8::Value> Call(int argc,
v8::Local<v8::Value> argv[],
AsyncResource* async_resource) const;
// Deprecated versions. Use the versions that accept an async_resource instead
// as they run the callback in the correct async context as specified by the
// resource. If you want to call a synchronous JS function (i.e. on a
// non-empty JS stack), you can use Nan::Call instead.
v8::Local<v8::Value> operator()(v8::Local<v8::Object> target,
int argc = 0,
v8::Local<v8::Value> argv[] = 0) const;
v8::Local<v8::Value> operator()(int argc = 0,
v8::Local<v8::Value> argv[] = 0) const;
v8::Local<v8::Value> Call(v8::Local<v8::Object> target,
int argc,
v8::Local<v8::Value> argv[]) const;
v8::Local<v8::Value> Call(int argc, v8::Local<v8::Value> argv[]) const;
};
```
Example usage:
```c++
v8::Local<v8::Function> function;
Nan::Callback callback(function);
callback.Call(0, 0);
```

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