74 lines
2.3 KiB
Markdown
74 lines
2.3 KiB
Markdown
## 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/io.js-3.3/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);
|
|
}
|
|
```
|
|
|