从 JS 中的回调函数调用类方法

Question

I'm having problem with the scope of 'this' in JS.
I have a callback function that calls a method (connectSensor). In that method, I try to change a member of the class using 'this'. However, I get
"TypeError: Cannot read property 'removeAllListeners()' of undefined".
I think because the method is called from inside the callback, 'this' no longer refers to the class, but I don't know how to solve it (ie have a reference to the class inside connectSensor). I'm using RPi 4 and Linux.

/* Perhipheral MAC. */
const SENSOR_MAC = "aa:aa:aa:aa:aa:aa";
class ble{

constructor(){
        this.noble = require('noble');
        this.sensor;    
}

createEventHandlers(){

        var noble = this.noble;

        
        noble.on('stateChange', function(state)
        {
                /* Start scanning if Bluetooth is on. */  
                if( state == 'poweredOn' ) noble.startScanning();

        });

        noble.on('discover', function(peripheral){
                if (perhipheral.address == SENSOR_MAC){
                        noble.stopScanning();
                        this.sensor = peripheral;
                        console.log("Discovered the sensor: " + this.sensor.name)
                        /* Here 'this' is bound to the class. */
                        this.connectSensor();
                }

        }.bind(this));
}

connectSensor(){
            /* I want 'this' here to always refer to the class. */
            this.sensor.removeAllListeners();
}

}

Usage:

bleClass = new ble();
bleClass.createEventHandlers();

Answer 1

I now realize the problem was that the connectSensor in my code (but not in the question) was outside the "if" statement. Therefore, the first BLE device to be discovered (which was never the intended sensor) did not have the "sensor" member initialized, and hence the error. In the end this had nothing to do with the scope of 'this' or JavaScript. I sincerely regret wasting everybody's time.