node-api: Add API to check safety of calling JS

Author: srriddle

doc/api/n-api.md

@@ -6295,6 +6295,24 @@ node_api_get_module_file_name(napi_env env, const char** result);
 `result` may be an empty string if the add-on loading process fails to establish
 the add-on's file name during loading.
 
+#### `napi_can_call_into_js`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+```c
+NAPI_EXTERN napi_status napi_can_call_into_js(napi_env env);
+```
+
+* `[in] env`: The environment that the API is invoked under.
+
+Returns `napi_ok` if the API succeeded.
+
+This API is used to check if it is safe to call into JavaScript.
+
 [ABI Stability]: https://nodejs.org/en/docs/guides/abi-stability/
 [AppVeyor]: https://www.appveyor.com
 [C++ Addons]: addons.md

src/js_native_api.h

@@ -566,6 +566,11 @@ NAPI_EXTERN napi_status NAPI_CDECL napi_object_seal(napi_env env,
                                                     napi_value object);
 #endif  // NAPI_VERSION >= 8
 
+#ifdef NAPI_EXPERIMENTAL
+NAPI_EXTERN napi_status NAPI_CDECL napi_can_call_into_js(napi_env env,
+                                                         bool* result);
+#endif
+
 EXTERN_C_END
 
 #endif  // SRC_JS_NATIVE_API_H_

src/js_native_api_v8.cc

@@ -3252,3 +3252,10 @@ napi_status NAPI_CDECL napi_is_detached_arraybuffer(napi_env env,
 
   return napi_clear_last_error(env);
 }
+
+napi_status NAPI_CDECL napi_can_call_into_js(napi_env env, bool* result) {
+  CHECK_ENV(env);
+  CHECK_ARG(env, result);
+  *result = (env)->can_call_into_js();
+  return napi_clear_last_error(env);
+}