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[VSoRC/.git] / node_modules / node-pty / node_modules / nan / doc / scopes.md

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+## 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-8.11/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);
+}
+```
+