| ## Scopes |
| |
| A _local handle_ is a pointer to an object. All V8 objects are accessed using handles, they are necessary because of the way the V8 garbage collector works. |
| |
| A handle scope can be thought of as a container for any number of handles. When you've finished with your handles, instead of deleting each one individually you can simply delete their scope. |
| |
| The creation of `HandleScope` objects is different across the supported versions of V8. Therefore, NAN provides its own implementations that can be used safely across these. |
| |
| - <a href="#api_nan_handle_scope"><b><code>Nan::HandleScope</code></b></a> |
| - <a href="#api_nan_escapable_handle_scope"><b><code>Nan::EscapableHandleScope</code></b></a> |
| |
| Also see the V8 Embedders Guide section on [Handles and Garbage Collection](https://github.com/v8/v8/wiki/Embedder%27s%20Guide#handles-and-garbage-collection). |
| |
| <a name="api_nan_handle_scope"></a> |
| ### Nan::HandleScope |
| |
| A simple wrapper around [`v8::HandleScope`](https://v8docs.nodesource.com/node-8.16/d3/d95/classv8_1_1_handle_scope.html). |
| |
| Definition: |
| |
| ```c++ |
| class Nan::HandleScope { |
| public: |
| Nan::HandleScope(); |
| static int NumberOfHandles(); |
| }; |
| ``` |
| |
| Allocate a new `Nan::HandleScope` whenever you are creating new V8 JavaScript objects. Note that an implicit `HandleScope` is created for you on JavaScript-accessible methods so you do not need to insert one yourself. |
| |
| Example: |
| |
| ```c++ |
| // new object is created, it needs a new scope: |
| void Pointless() { |
| Nan::HandleScope scope; |
| v8::Local<v8::Object> obj = Nan::New<v8::Object>(); |
| } |
| |
| // JavaScript-accessible method already has a HandleScope |
| NAN_METHOD(Pointless2) { |
| v8::Local<v8::Object> obj = Nan::New<v8::Object>(); |
| } |
| ``` |
| |
| <a name="api_nan_escapable_handle_scope"></a> |
| ### Nan::EscapableHandleScope |
| |
| Similar to [`Nan::HandleScope`](#api_nan_handle_scope) but should be used in cases where a function needs to return a V8 JavaScript type that has been created within it. |
| |
| Definition: |
| |
| ```c++ |
| class Nan::EscapableHandleScope { |
| public: |
| Nan::EscapableHandleScope(); |
| static int NumberOfHandles(); |
| template<typename T> v8::Local<T> Escape(v8::Local<T> value); |
| } |
| ``` |
| |
| Use `Escape(value)` to return the object. |
| |
| Example: |
| |
| ```c++ |
| v8::Local<v8::Object> EmptyObj() { |
| Nan::EscapableHandleScope scope; |
| v8::Local<v8::Object> obj = Nan::New<v8::Object>(); |
| return scope.Escape(obj); |
| } |
| ``` |
| |