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mamingshuai e95417854b update OpenHarmony 2.0 Canary
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# NAPI<a name="EN-US_TOPIC_0000001149901711"></a>
- [Introduction](#section11660541593)
- [Directory Structure](#section161941989596)
- [When to Use](#section11759141594811)
- [Available APIs](#section1611515555510)
- [How to Develop](#section937267212)
- [Repositories Involved](#section3970193518214)
## Introduction<a name="section11660541593"></a>
The **foundation/ace/napi** repository contains a development framework for extending the JS Native Module and provides APIs developed based on Node.js N-API for external use.
**Figure 1** Architecture<a name="fig1049423884819"></a>
![](figures/en-us_image_0000001162437581.png)
- **NativeEngine**
NativeEngine is the JS engine abstraction layer. It unifies API behavior of the JS engines at the NAPI layer.
- **ModuleManager**
ModuleManager is used to load modules and cache module information.
- **ScopeManager**
ScopeManager manages the NativeValue lifecycle.
- **ReferenceManager**
ReferenceManager manages the NativeReference lifecycle.
## Directory Structure<a name="section161941989596"></a>
The source code directory structure of this repository is as follows:
```
foundation/ace/napi
├── interfaces
│ └── kits
│ └── napi # NAPI header files
├── module_manager # Module manager
├── native_engine # NativeEngine abstraction layer
│ └── impl
│ └── quickjs # QuickJS-based NativeEngine implementation
├── scope_manager # Scope manager
└── test # Test code
```
## When to Use<a name="section11759141594811"></a>
NAPI is suitable for processing I/O- and CPU-intensive tasks and system tasks. It encapsulates the capabilities and provides them to apps as JS APIs. NAPI can be used to implement mutual access between JS and C/C++ code. You can use NAPI to develop modules such as network communications, serial port access, multimedia decoding, and sensor data collection.
## Available APIs<a name="section1611515555510"></a>
For details about the API implementation, see the **foundation/ace/napi** repository.
**Table 1** Available NAPIs
<a name="table10789351555"></a>
<table><thead align="left"><tr id="row1878635175515"><th class="cellrowborder" valign="top" width="19.439999999999998%" id="mcps1.2.3.1.1"><p id="p27816352556"><a name="p27816352556"></a><a name="p27816352556"></a>Category</p>
</th>
<th class="cellrowborder" valign="top" width="80.56%" id="mcps1.2.3.1.2"><p id="p078835105514"><a name="p078835105514"></a><a name="p078835105514"></a>Description</p>
</th>
</tr>
</thead>
<tbody><tr id="row17863535520"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p678143512552"><a name="p678143512552"></a><a name="p678143512552"></a>Module registration</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p4781035185515"><a name="p4781035185515"></a><a name="p4781035185515"></a>Registers module information with a manager.</p>
</td>
</tr>
<tr id="row67951538205618"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p127961438195616"><a name="p127961438195616"></a><a name="p127961438195616"></a>Exception &amp; Error handling</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p47961338195617"><a name="p47961338195617"></a><a name="p47961338195617"></a>Throws exceptions.</p>
</td>
</tr>
<tr id="row778417510579"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p1878575185715"><a name="p1878575185715"></a><a name="p1878575185715"></a>Object lifecycle</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p1178565175711"><a name="p1178565175711"></a><a name="p1178565175711"></a>Manages NAPI object lifecycle within limited scopes.</p>
</td>
</tr>
<tr id="row83179619572"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p1531786125717"><a name="p1531786125717"></a><a name="p1531786125717"></a>JS object</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p12317663572"><a name="p12317663572"></a><a name="p12317663572"></a>Creates standard object types.</p>
</td>
</tr>
<tr id="row63859616579"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p438696165720"><a name="p438696165720"></a><a name="p438696165720"></a>C-to-NAPI</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p14386462570"><a name="p14386462570"></a><a name="p14386462570"></a>Converts data types from C to NAPI.</p>
</td>
</tr>
<tr id="row1145119612578"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p13451116115716"><a name="p13451116115716"></a><a name="p13451116115716"></a>NAPI-to-C</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p12451464574"><a name="p12451464574"></a><a name="p12451464574"></a>Converts data types from NAPI to C.</p>
</td>
</tr>
<tr id="row1451436155720"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p155147625713"><a name="p155147625713"></a><a name="p155147625713"></a>Global instance</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p551466195713"><a name="p551466195713"></a><a name="p551466195713"></a>Obtains global instances.</p>
</td>
</tr>
<tr id="row65815617579"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p458119617577"><a name="p458119617577"></a><a name="p458119617577"></a>JS value</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p125818625711"><a name="p125818625711"></a><a name="p125818625711"></a>Provides APIs executing <strong id="b18893622126"><a name="b18893622126"></a><a name="b18893622126"></a>===</strong>, <strong id="b5190121451212"><a name="b5190121451212"></a><a name="b5190121451212"></a>typeof</strong>, <strong id="b01299162121"><a name="b01299162121"></a><a name="b01299162121"></a>instanceof</strong>, and other operations alike.</p>
</td>
</tr>
<tr id="row10649166145711"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p18649196195716"><a name="p18649196195716"></a><a name="p18649196195716"></a>JS object property</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p164919615574"><a name="p164919615574"></a><a name="p164919615574"></a>Provides functions for performing operations on object properties.</p>
</td>
</tr>
<tr id="row0714260574"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p37143675714"><a name="p37143675714"></a><a name="p37143675714"></a>JS function</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p771466115711"><a name="p771466115711"></a><a name="p771466115711"></a>Invokes functions and creates instances.</p>
</td>
</tr>
<tr id="row1578176155717"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p1782126155711"><a name="p1782126155711"></a><a name="p1782126155711"></a>Object encapsulation</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p87821967572"><a name="p87821967572"></a><a name="p87821967572"></a>Binds the external context of JS objects.</p>
</td>
</tr>
<tr id="row8854116105717"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p1685414619578"><a name="p1685414619578"></a><a name="p1685414619578"></a>Simple asynchronization</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p1685411612574"><a name="p1685411612574"></a><a name="p1685411612574"></a>Creates asynchronous tasks.</p>
</td>
</tr>
<tr id="row109154635718"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p391556195720"><a name="p391556195720"></a><a name="p391556195720"></a>Promise</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p1091566135717"><a name="p1091566135717"></a><a name="p1091566135717"></a>Creates a function set for a promise.</p>
</td>
</tr>
<tr id="row1671493313016"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.2.3.1.1 "><p id="p1971512331709"><a name="p1971512331709"></a><a name="p1971512331709"></a>Script</p>
</td>
<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.2.3.1.2 "><p id="p371517332013"><a name="p371517332013"></a><a name="p371517332013"></a>Runs JS code.</p>
</td>
</tr>
</tbody>
</table>
## How to Develop<a name="section937267212"></a>
The following example describes how to use NAPI to develop a JS API for obtaining the application bundle name.
The prototype of the JS API is as follows:
```
function getAppName(): string;
```
The implementation code of the JS API is as follows:
```
// app.cpp
#include <stdio.h>
#include <string.h>
#include "napi/native_api.h"
#include "napi/native_node_api.h"
struct AsyncCallbackInfo {
napi_env env;
napi_async_work asyncWork;
napi_deferred deferred;
};
// C/C++ function corresponding to getAppName()
napi_value JSGetAppName(napi_env env, napi_callback_info info) {
napi_deferred deferred;
napi_value promise;
// Create a promise.
NAPI_CALL(env, napi_create_promise(env, &deferred, &promise));
AsyncCallbackInfo* asyncCallbackInfo = new AsyncCallbackInfo {
.env = env,
.asyncWork = nullptr,
.deferred = deferred,
};
napi_value resourceName;
napi_create_string_latin1(env, "GetAppName", NAPI_AUTO_LENGTH, &resourceName);
// Create a queue of asynchronous tasks.
napi_create_async_work(
env, nullptr, resourceName,
// Callback for an asynchronous task
[](napi_env env, void* data) {},
// Callback after the asynchronous task is complete
[](napi_env env, napi_status status, void* data) {
AsyncCallbackInfo* asyncCallbackInfo = (AsyncCallbackInfo*)data;
napi_value appName;
const char* str = "com.example.helloworld";
napi_create_string_utf8(env, str, strlen(str), &appName);
// Trigger the callback.
napi_resolve_deferred(asyncCallbackInfo->env, asyncCallbackInfo->deferred, appName);
napi_delete_async_work(env, asyncCallbackInfo->asyncWork);
delete asyncCallbackInfo;
},
(void*)asyncCallbackInfo, &asyncCallbackInfo->asyncWork);
napi_queue_async_work(env, asyncCallbackInfo->asyncWork);
return promise;
}
// Export the module.
static napi_value AppExport(napi_env env, napi_value exports)
{
static napi_property_descriptor desc[] = {
DECLARE_NAPI_FUNCTION("getAppName", JSGetAppName),
};
NAPI_CALL(env, napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc));
return exports;
}
// App module description
static napi_module appModule = {
.nm_version = 1,
.nm_flags = 0,
.nm_filename = nullptr,
.nm_register_func = AppExport,
.nm_modname = "app",
.nm_priv = ((void*)0),
.reserved = {0}
};
// Register the module.
extern "C" __attribute__((constructor)) void AppRegister()
{
napi_module_register(&appModule);
}
```
The build script is as follows:
```
// BUILD.gn
import("//build/ohos.gni")
ohos_shared_library("app") {
# Specify the source file to build.
sources = [
"app.cpp",
]
# Specify build dependencies.
deps = [ "//foundation/ace/napi:ace_napi" ]
# Specify the directory where the library is generated.
relative_install_dir = "module"
subsystem_name = "ace"
part_name = "napi"
}
```
Test code to run in your app is as follows:
```
import app from '@ohos.app'
export default {
testGetAppName() {
app.getAppName().then(function (data) {
console.info('app name: ' + data);
});
}
}
```
## Repositories Involved<a name="section3970193518214"></a>
JS UI framework
ace\_ace\_engine
ace\_ace\_engine\_lite
**ace\_napi**
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