1# Env
2
3The opaque data structure containing the environment in which the request is being run.
4
5The Env object is usually created and passed by the Node.js runtime or node-addon-api infrastructure.
6
7## Methods
8
9### Constructor
10
11```cpp
12Napi::Env::Env(napi_env env);
13```
14
15- `[in] env`: The `napi_env` environment from which to construct the `Napi::Env` object.
16
17### napi_env
18
19```cpp
20operator napi_env() const;
21```
22
23Returns the `napi_env` opaque data structure representing the environment.
24
25### Global
26
27```cpp
28Napi::Object Napi::Env::Global() const;
29```
30
31Returns the `Napi::Object` representing the environment's JavaScript Global Object.
32
33### Undefined
34
35```cpp
36Napi::Value Napi::Env::Undefined() const;
37```
38
39Returns the `Napi::Value` representing the environment's JavaScript Undefined Object.
40
41### Null
42
43```cpp
44Napi::Value Napi::Env::Null() const;
45```
46
47Returns the `Napi::Value` representing the environment's JavaScript Null Object.
48
49### IsExceptionPending
50
51```cpp
52bool Napi::Env::IsExceptionPending() const;
53```
54
55Returns a `bool` indicating if an exception is pending in the environment.
56
57### GetAndClearPendingException
58
59```cpp
60Napi::Error Napi::Env::GetAndClearPendingException() const;
61```
62
63Returns an `Napi::Error` object representing the environment's pending exception, if any.
64
65### RunScript
66
67```cpp
68Napi::Value Napi::Env::RunScript(____ script) const;
69```
70- `[in] script`: A string containing JavaScript code to execute.
71
72Runs JavaScript code contained in a string and returns its result.
73
74The `script` can be any of the following types:
75- [`Napi::String`](string.md)
76- `const char *`
77- `const std::string &`
78
79### GetInstanceData
80```cpp
81template <typename T> T* GetInstanceData() const;
82```
83
84Returns the instance data that was previously associated with the environment,
85or `nullptr` if none was associated.
86
87### SetInstanceData
88
89```cpp
90template <typename T> using Finalizer = void (*)(Env, T*);
91template <typename T, Finalizer<T> fini = Env::DefaultFini<T>>
92void SetInstanceData(T* data) const;
93```
94
95- `[template] fini`: A function to call when the instance data is to be deleted.
96Accepts a function of the form `void CleanupData(Napi::Env env, T* data)`. If
97not given, the default finalizer will be used, which simply uses the `delete`
98operator to destroy `T*` when the addon instance is unloaded.
99- `[in] data`: A pointer to data that will be associated with the instance of
100the addon for the duration of its lifecycle.
101
102Associates a data item stored at `T* data` with the current instance of the
103addon. The item will be passed to the function `fini` which gets called when an
104instance of the addon is unloaded.
105
106### SetInstanceData
107
108```cpp
109template <typename DataType, typename HintType>
110using FinalizerWithHint = void (*)(Env, DataType*, HintType*);
111template <typename DataType,
112          typename HintType,
113          FinalizerWithHint<DataType, HintType> fini =
114            Env::DefaultFiniWithHint<DataType, HintType>>
115void SetInstanceData(DataType* data, HintType* hint) const;
116```
117
118- `[template] fini`: A function to call when the instance data is to be deleted.
119Accepts a function of the form
120`void CleanupData(Napi::Env env, DataType* data, HintType* hint)`. If not given,
121the default finalizer will be used, which simply uses the `delete` operator to
122destroy `T*` when the addon instance is unloaded.
123- `[in] data`: A pointer to data that will be associated with the instance of
124the addon for the duration of its lifecycle.
125- `[in] hint`: A pointer to data that will be associated with the instance of
126the addon for the duration of its lifecycle and will be passed as a hint to
127`fini` when the addon instance is unloaded.
128
129Associates a data item stored at `T* data` with the current instance of the
130addon. The item will be passed to the function `fini` which gets called when an
131instance of the addon is unloaded. This overload accepts an additional hint to
132be passed to `fini`.
133
134### GetModuleFileName
135
136```cpp
137const char* Napi::Env::GetModuleFileName() const;
138```
139
140Returns a A URL containing the absolute path of the location from which the
141add-on was loaded. For a file on the local file system it will start with
142`file://`. The string is null-terminated and owned by env and must thus not be
143modified or freed. It is only valid while the add-on is loaded.
144
145### AddCleanupHook
146
147```cpp
148template <typename Hook>
149CleanupHook<Hook> AddCleanupHook(Hook hook);
150```
151
152- `[in] hook`: A function to call when the environment exits. Accepts a
153  function of the form `void ()`.
154
155Registers `hook` as a function to be run once the current Node.js environment
156exits. Unlike the underlying C-based Node-API, providing the same `hook`
157multiple times **is** allowed. The hooks will be called in reverse order, i.e.
158the most recently added one will be called first.
159
160Returns an `Env::CleanupHook` object, which can be used to remove the hook via
161its `Remove()` method.
162
163### AddCleanupHook
164
165```cpp
166template <typename Hook, typename Arg>
167CleanupHook<Hook, Arg> AddCleanupHook(Hook hook, Arg* arg);
168```
169
170- `[in] hook`: A function to call when the environment exits. Accepts a
171  function of the form `void (Arg* arg)`.
172- `[in] arg`: A pointer to data that will be passed as the argument to `hook`.
173
174Registers `hook` as a function to be run with the `arg` parameter once the
175current Node.js environment exits. Unlike the underlying C-based Node-API,
176providing the same `hook` and `arg` pair multiple times **is** allowed. The
177hooks will be called in reverse order, i.e. the most recently added one will be
178called first.
179
180Returns an `Env::CleanupHook` object, which can be used to remove the hook via
181its `Remove()` method.
182
183# Env::CleanupHook
184
185The `Env::CleanupHook` object allows removal of the hook added via
186`Env::AddCleanupHook()`
187
188## Methods
189
190### IsEmpty
191
192```cpp
193bool IsEmpty();
194```
195
196Returns `true` if the cleanup hook was **not** successfully registered.
197
198### Remove
199
200```cpp
201bool Remove(Env env);
202```
203
204Unregisters the hook from running once the current Node.js environment exits.
205
206Returns `true` if the hook was successfully removed from the Node.js
207environment.
208