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74 lines
2.3 KiB
74 lines
2.3 KiB
1 month ago
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## Scopes
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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.
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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.
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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.
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- <a href="#api_nan_handle_scope"><b><code>Nan::HandleScope</code></b></a>
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- <a href="#api_nan_escapable_handle_scope"><b><code>Nan::EscapableHandleScope</code></b></a>
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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).
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<a name="api_nan_handle_scope"></a>
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### Nan::HandleScope
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A simple wrapper around [`v8::HandleScope`](https://v8docs.nodesource.com/node-8.16/d3/d95/classv8_1_1_handle_scope.html).
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Definition:
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```c++
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class Nan::HandleScope {
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public:
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Nan::HandleScope();
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static int NumberOfHandles();
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};
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```
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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.
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Example:
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```c++
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// new object is created, it needs a new scope:
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void Pointless() {
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Nan::HandleScope scope;
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v8::Local<v8::Object> obj = Nan::New<v8::Object>();
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}
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// JavaScript-accessible method already has a HandleScope
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NAN_METHOD(Pointless2) {
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v8::Local<v8::Object> obj = Nan::New<v8::Object>();
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}
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```
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<a name="api_nan_escapable_handle_scope"></a>
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### Nan::EscapableHandleScope
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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.
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Definition:
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```c++
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class Nan::EscapableHandleScope {
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public:
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Nan::EscapableHandleScope();
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static int NumberOfHandles();
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template<typename T> v8::Local<T> Escape(v8::Local<T> value);
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}
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```
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Use `Escape(value)` to return the object.
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Example:
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```c++
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v8::Local<v8::Object> EmptyObj() {
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Nan::EscapableHandleScope scope;
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v8::Local<v8::Object> obj = Nan::New<v8::Object>();
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return scope.Escape(obj);
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}
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```
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