程序代写代做代考 Java javascript ## Scopes
## 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.
– Nan::HandleScope
– Nan::EscapableHandleScope
Also see the V8 Embedders Guide section on [Handles and Garbage Collection](https://developers.google.com/v8/embed#handles).
A simple wrapper around [`v8::HandleScope`](https://v8docs.nodesource.com/io.js-3.0/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
}
// JavaScript-accessible method already has a HandleScope
NAN_METHOD(Pointless2) {
v8::Local
}
“`
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
}
“`
Use `Escape(value)` to return the object.
Example:
“`c++
v8::Local
Nan::EscapableHandleScope scope;
v8::Local
return scope.Escape(obj);
}
“`