（已解决）打字稿/ MQTT /节点-如何从回调函数访问类成员？

debugcn 发表于 Dev

安东尼·费里

我正在制作一个应用程序来管理我家里的一些智能灯。

我创建了一个非常简单的Broker类。

import * as aedes from 'aedes';
import * as net from 'net';

export class Broker {

    aedes: aedes.Aedes;
    broker: net.Server;
    port: number;

    constructor(port: number){
        this.aedes = aedes();
        this.broker = net.createServer(this.aedes.handle);
        this.port = port;
        this.broker.listen(this.port, () => {
            console.log('MQTT is listening.');
        });
    }
    
    /** 
     * This is a callback register function
     *
     * Callback function must have a signature of type : function(topic: string, payload: string)
     **/
    onMsgReceived(callback: {(topic: string, payload: string): void}){
        this.aedes.on('publish', (packet, client) => {
            if (packet.cmd != 'publish') return;
            callback(packet.topic, packet.payload.toString());
        });
    }

}

然后，例如，一个Test类。

export Test {
    someVar: string;
    
    constructor(){ }
    
    onMsgReceivedCallback(topic: string, payload: string){
        console.log('Hey, i\'m printed from the test class');
        console.log('And this is some var : ' + this.someVar);
    }
}

当然还有index.ts脚本。

import { Broker } from './broker.ts'
import { Test } from './test.ts'

const broker = new Broker(1883);
const test   = new Test();


broker.onMsgReceived(test.onMsgReceivedCallback);

问题是，如果在函数中test.onMsgReceived我想调用该类的成员（如var）someVar，则节点将抛出以下错误：

TypeError: Cannot read property 'testVar' of undefined

我不明白如何解决此错误...您有想法吗？

Dmytro

如果要将this类实例的上下文作为回调传递，则必须将其绑定到方法。有两种方法可以在TypeScript中执行此操作。

使用箭头功能定义方法：

export Test {
    someVar: string;

    constructor() {}

    onMsgReceivedCallback = (topic: string, payload: string) => {
        console.log(`someVar: ${this.someVar}`);
    }
}

或在构造函数中绑定方法：

export Test {
    someVar: string;

    constructor() {
        this.onMsgReceivedCallback = this.onMsgReceivedCallback.bind(this);
    }

    onMsgReceivedCallback(topic: string, payload: string) {
        console.log(`someVar: ${this.someVar}`);
    }
}

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