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+# AsyncWorker
+
+`Napi::AsyncWorker` is an abstract class that you can subclass to remove many of
+the tedious tasks of moving data between the event loop and worker threads. This
+class internally handles all the details of creating and executing an asynchronous
+operation.
+
+Once created, execution is requested by calling `Napi::AsyncWorker::Queue`. When
+a thread is available for execution the `Napi::AsyncWorker::Execute` method will
+be invoked. Once `Napi::AsyncWorker::Execute` completes either
+`Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` will be invoked. Once
+the `Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` methods are
+complete the `Napi::AsyncWorker` instance is destructed.
+
+For the most basic use, only the `Napi::AsyncWorker::Execute` method must be
+implemented in a subclass.
+
+## Methods
+
+### Env
+
+Requests the environment in which the async worker has been initially created.
+
+```cpp
+Napi::Env Napi::AsyncWorker::Env() const;
+```
+
+Returns the environment in which the async worker has been created.
+
+### Queue
+
+Requests that the work be queued for execution.
+
+```cpp
+void Napi::AsyncWorker::Queue();
+```
+
+### Cancel
+
+Cancels queued work if it has not yet been started. If it has already started
+executing, it cannot be cancelled. If cancelled successfully neither
+`OnOK` nor `OnError` will be called.
+
+```cpp
+void Napi::AsyncWorker::Cancel();
+```
+
+### Receiver
+
+```cpp
+Napi::ObjectReference& Napi::AsyncWorker::Receiver();
+```
+
+Returns the persistent object reference of the receiver object set when the async
+worker was created.
+
+### Callback
+
+```cpp
+Napi::FunctionReference& Napi::AsyncWorker::Callback();
+```
+
+Returns the persistent function reference of the callback set when the async
+worker was created. The returned function reference will receive the results of
+the computation that happened in the `Napi::AsyncWorker::Execute` method, unless
+the default implementation of `Napi::AsyncWorker::OnOK` or
+`Napi::AsyncWorker::OnError` is overridden.
+
+### SuppressDestruct
+
+```cpp
+void Napi::AsyncWorker::SuppressDestruct();
+```
+
+Prevents the destruction of the `Napi::AsyncWorker` instance upon completion of
+the `Napi::AsyncWorker::OnOK` callback.
+
+### SetError
+
+Sets the error message for the error that happened during the execution. Setting
+an error message will cause the `Napi::AsyncWorker::OnError` method to be
+invoked instead of `Napi::AsyncWorker::OnOK` once the
+`Napi::AsyncWorker::Execute` method completes.
+
+```cpp
+void Napi::AsyncWorker::SetError(const std::string& error);
+```
+
+- `[in] error`: The reference to the string that represent the message of the error.
+
+### Execute
+
+This method is used to execute some tasks outside of the **event loop** on a libuv
+worker thread. Subclasses must implement this method and the method is run on
+a thread other than that running the main event loop. As the method is not
+running on the main event loop, it must avoid calling any methods from node-addon-api
+or running any code that might invoke JavaScript. Instead, once this method is
+complete any interaction through node-addon-api with JavaScript should be implemented
+in the `Napi::AsyncWorker::OnOK` method and `Napi::AsyncWorker::OnError` which run
+on the main thread and are invoked when the `Napi::AsyncWorker::Execute` method completes.
+
+```cpp
+virtual void Napi::AsyncWorker::Execute() = 0;
+```
+
+### OnOK
+
+This method is invoked when the computation in the `Execute` method ends.
+The default implementation runs the `Callback` optionally provided when the
+`AsyncWorker` class was created. The `Callback` will by default receive no
+arguments. The arguments to the `Callback` can be provided by overriding the
+`GetResult()` method.
+
+```cpp
+virtual void Napi::AsyncWorker::OnOK();
+```
+### GetResult
+
+This method returns the arguments passed to the `Callback` invoked by the default
+`OnOK()` implementation. The default implementation returns an empty vector,
+providing no arguments to the `Callback`.
+
+```cpp
+virtual std::vector<napi_value> Napi::AsyncWorker::GetResult(Napi::Env env);
+```
+
+### OnError
+
+This method is invoked after `Napi::AsyncWorker::Execute` completes if an error
+occurs while `Napi::AsyncWorker::Execute` is running and C++ exceptions are
+enabled or if an error was set through a call to `Napi::AsyncWorker::SetError`.
+The default implementation calls the `Callback` provided when the `Napi::AsyncWorker`
+class was created, passing in the error as the first parameter.
+
+```cpp
+virtual void Napi::AsyncWorker::OnError(const Napi::Error& e);
+```
+
+### Destroy
+
+This method is invoked when the instance must be deallocated. If
+`SuppressDestruct()` was not called then this method will be called after either
+`OnError()` or `OnOK()` complete. The default implementation of this method
+causes the instance to delete itself using the `delete` operator. The method is
+provided so as to ensure that instances allocated by means other than the `new`
+operator can be deallocated upon work completion.
+
+```cpp
+virtual void Napi::AsyncWorker::Destroy();
+```
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Function& callback);
+```
+
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by calling
+`Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Function& callback, const char* resource_name);
+```
+
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Function& callback, const char* resource_name, const Napi::Object& resource);
+```
+
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+- `[in] resource`: Object associated with the asynchronous operation that
+will be passed to possible async_hooks.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback);
+```
+
+- `[in] receiver`: The `this` object passed to the called function.
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback, const char* resource_name);
+```
+
+- `[in] receiver`: The `this` object passed to the called function.
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+
+Returns a `Napi::AsyncWork` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback, const char* resource_name, const Napi::Object& resource);
+```
+
+- `[in] receiver`: The `this` object passed to the called function.
+- `[in] callback`: The function which will be called when an asynchronous
+operations ends. The given function is called from the main event loop thread.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+- `[in] resource`: Object associated with the asynchronous operation that
+will be passed to possible async_hooks.
+
+Returns a `Napi::AsyncWork` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(Napi::Env env);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
+
+Returns an `Napi::AsyncWorker` instance which can later be queued for execution by calling
+`Napi::AsyncWorker::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(Napi::Env env, const char* resource_name);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWorker::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncWorker`.
+
+```cpp
+explicit Napi::AsyncWorker(Napi::Env env, const char* resource_name, const Napi::Object& resource);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
+- `[in] resource_name`: Null-terminated string that represents the
+identifier for the kind of resource that is being provided for diagnostic
+information exposed by the async_hooks API.
+- `[in] resource`: Object associated with the asynchronous operation that
+will be passed to possible async_hooks.
+
+Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWorker::Queue`.
+
+### Destructor
+
+Deletes the created work object that is used to execute logic asynchronously.
+
+```cpp
+virtual Napi::AsyncWorker::~AsyncWorker();
+```
+
+## Operator
+
+```cpp
+Napi::AsyncWorker::operator napi_async_work() const;
+```
+
+Returns the N-API napi_async_work wrapped by the `Napi::AsyncWorker` object. This
+can be used to mix usage of the C N-API and node-addon-api.
+
+## Example
+
+The first step to use the `Napi::AsyncWorker` class is to create a new class that
+inherits from it and implement the `Napi::AsyncWorker::Execute` abstract method.
+Typically input to your worker will be saved within class' fields generally
+passed in through its constructor.
+
+When the `Napi::AsyncWorker::Execute` method completes without errors the
+`Napi::AsyncWorker::OnOK` function callback will be invoked. In this function the
+results of the computation will be reassembled and returned back to the initial
+JavaScript context.
+
+`Napi::AsyncWorker` ensures that all the code in the `Napi::AsyncWorker::Execute`
+function runs in the background out of the **event loop** thread and at the end
+the `Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` function will be
+called and are executed as part of the event loop.
+
+The code below shows a basic example of `Napi::AsyncWorker` the implementation:
+
+```cpp
+#include<napi.h>
+
+#include <chrono>
+#include <thread>
+
+use namespace Napi;
+
+class EchoWorker : public AsyncWorker {
+    public:
+        EchoWorker(Function& callback, std::string& echo)
+        : AsyncWorker(callback), echo(echo) {}
+
+        ~EchoWorker() {}
+    // This code will be executed on the worker thread
+    void Execute() {
+        // Need to simulate cpu heavy task
+        std::this_thread::sleep_for(std::chrono::seconds(1));
+    }
+
+    void OnOK() {
+        HandleScope scope(Env());
+        Callback().Call({Env().Null(), String::New(Env(), echo)});
+    }
+
+    private:
+        std::string echo;
+};
+```
+
+The `EchoWorker`'s contructor calls the base class' constructor to pass in the
+callback that the `Napi::AsyncWorker` base class will store persistently. When
+the work on the `Napi::AsyncWorker::Execute` method is done the
+`Napi::AsyncWorker::OnOk` method is called and the results return back to
+JavaScript invoking the stored callback with its associated environment.
+
+The following code shows an example of how to create and use an `Napi::AsyncWorker`.
+
+```cpp
+#include<napi.h>
+
+// Include EchoWorker class
+// ..
+
+use namespace Napi;
+
+Value Echo(const CallbackInfo& info) {
+    // You need to validate the arguments here.
+    Function cb = info[1].As<Function>();
+    std::string in = info[0].As<String>();
+    EchoWorker* wk = new EchoWorker(cb, in);
+    wk->Queue();
+    return info.Env().Undefined();
+```
+
+Using the implementation of a `Napi::AsyncWorker` is straight forward. You only
+need to create a new instance and pass to its constructor the callback you want to
+execute when your asynchronous task ends and other data you need for your
+computation. Once created the only other action you have to do is to call the
+`Napi::AsyncWorker::Queue` method that will queue the created worker for execution.