回调
插件中的常见做法是将 JavaScript 函数传给 C++ 函数并从那里执行它们。 以下示例说明了如何调用此类回调:
// addon.cc
#include <node.h>
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = {
String::NewFromUtf8(isolate,
"hello world").ToLocalChecked() };
cb->Call(context, Null(isolate), argc, argv).ToLocalChecked();
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
此示例使用 Init()
的双参数形式,它接收完整的 module
对象作为第二个参数。
这允许插件使用单个函数完全覆盖 exports
,而不是将该函数添加为 exports
的属性。
要测试它,则运行以下 JavaScript:
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg);
// 打印: 'hello world'
});
在这个例子中,回调函数是同步调用的。
It is common practice within addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks:
// addon.cc
#include <node.h>
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = {
String::NewFromUtf8(isolate,
"hello world").ToLocalChecked() };
cb->Call(context, Null(isolate), argc, argv).ToLocalChecked();
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(NODE_GYP_MODULE_NAME, Init)
} // namespace demo
This example uses a two-argument form of Init()
that receives the full
module
object as the second argument. This allows the addon to completely
overwrite exports
with a single function instead of adding the function as a
property of exports
.
To test it, run the following JavaScript:
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg);
// Prints: 'hello world'
});
In this example, the callback function is invoked synchronously.