nodejs回调问题(settimeout()

Question

我是Nodejs中开发Raspberry Pi 3服务器的新手。最近，我开始使用蓝牙BLE技术在NodeJS上工作，我编写了一台服务器来发送响应和通知。将任何响应通知发送回连接的设备是我的nodejs代码，我正在使用bleno.js库以ble回调

To send response back to the caller
function updateCallback(ref, msg=""){
    if (ref._updateValueCallback) {
        console.log('Response value : '+msg);
        ref._updateValueCallback(ref._value);
    }
}
if(tokens[2]=="1"){
    func.storeRelayAction(db, "1", decryptedString).then(result => {
        this._value = Buffer.from(result.toString(), 'utf8');
        updateCallback(this,result.toString()); // Send proper call back to device
    }).then(()=>{
        unlockTrigger();
        var timer = func.getTimer(db);
        timer.then(delayTime=>{
            console.log(delayTime + "::delayTime");
            if(delayTime){
                setTimeout(function(){
                    lockTrigger();
                    console.log("after sleep");
                    this._value = Buffer.from("1", 'utf8');
                    updateCallback(this,"1");// Not Working from here
                },parseInt(delayTime)*1000)
            }
        })
    })
}

如果我将updateCallback（this，" 1"）移动到settimeout funcation之外，则它可以完美地工作

Answer 1

问题似乎与setTimeout中的this绑定有关。使用箭头功能或使用

之类的东西

const self = this在Settimeout（）之前，在Settimeout中使用self而不是this。

function updateCallback(ref, msg = "") {
  if (ref._updateValueCallback) {
    console.log('Response value : ' + msg);
    ref._updateValueCallback(ref._value);
  }
}
if (tokens[2] == "1") {
  func.storeRelayAction(db, "1", decryptedString).then(result => {
    this._value = Buffer.from(result.toString(), 'utf8');
    updateCallback(this, result.toString()); // Send proper call back to device
  }).then(() => {
    unlockTrigger();
    var timer = func.getTimer(db);
    timer.then(delayTime => {
      console.log(delayTime + "::delayTime");
      if (delayTime) {
        //use an arrow fn here
        setTimeout( () => {
          lockTrigger();
          console.log("after sleep");
          this._value = Buffer.from("1", 'utf8');
          updateCallback(this, "1"); // Not Working from here
        }, parseInt(delayTime) * 1000)

      }
    })
  })
}