Question

嗨，我已经编写了此功能。

GetIndex方法

  getIndex(req: connreq){
  var found = false;
  var number =0;
  this.firereq.child(req.recipient).once('value', function(snapshot) {
    if (!snapshot.exists()) {
      console.log('Not exists');
      this.x = '0';
    }
  });

  }

在这个函数中，我称之为它。

SendCommand方法

 async sendcommand(req: connreq, cmd: string) {
this.getIndex(req);
  var promise = new Promise((resolve, reject) => {
    this.firereq
    .child(req.recipient)
    .child(this.x) .set({
      sender: req.sender,
      Command: cmd,
    })
    .then(() => {
      resolve({ success: true });
    })
    .catch(err => {
      resolve(err);
    });
    });
      return promise;


}

但是，第二个函数似乎在getIndex方法完成之前就继续执行。我假设我们可以使用awaits和promises来强制sendcommand函数在完成其余任务之前等待Getindex完成。任何帮助将不胜感激

Answer 1

在getIndex（）方法中返回一个promise，然后在中执行第二个，然后进行回调。因此，通常，getIndex应该是：

getIndex(req: connreq){
    return new Promise((resolve,reject) =>
    {
        var found = false;
        var number =0;
        this.firereq.child(req.recipient).once('value', 
        function(snapshot) {
           if (!snapshot.exists()) {
               console.log('Not exists');
               this.x = '0';
               reject('Not exists');
            }
            resolve('exists');
        });
     });
}

如果找不到，上述内容将触发catch块，如果找到则将触发then块：

this.getIndex(req)
.then(() => {
    this.firereq
    .child(req.recipient)
    .child(this.x) .set({
          sender: req.sender,
          Command: cmd,
    })
    .then(() => {
       resolve({ success: true });
     })
    .catch(err => {
       resolve(err);
    })
})
.catch(err => {
  resolve(err);
});

Answer 2

在第一个功能中，请执行以下操作：

 getIndex(req: connreq){
  return new Promise((resolve, reject) =>
  let found = false;
  let number =0;
  this.firereq.child(req.recipient).once('value', function(snapshot) {
    if (!snapshot.exists()) {
       reject("not exists");
      console.log('Not exists');
      this.x = '0';
       }
    else{
       resolve(snapshot.val());
         }
      });
    });
  }

那么您可以做：

 async sendcommand(req: connreq, cmd: string) {
this.getIndex(req).then((data)=>
  {
  var promise = new Promise((resolve, reject) => {
    this.firereq
    .child(req.recipient)
    .child(this.x) .set({
      sender: req.sender,
      Command: cmd,
    })
    .then(() => {
      resolve({ success: true });
    })
    .catch(err => {
      resolve(err);
    });
    });
    });
      return promise;


}

通过这种方式，getIndex()将返回一个诺言，并且then()返回之后将执行所有insde getIndex()。

Answer 3

从Promise返回getIndex，并在await函数中返回sendCommand

    getIndex(req: connreq){
      return new Promise((resolve, reject) => {
      var found = false;
      var number =0;
      this.firereq.child(req.recipient).once('value', function(snapshot) {
        if (!snapshot.exists()) {
          console.log('Not exists');
          this.x = '0';
        }
      });

      resolve();
      }
    });

和

    async sendcommand(req: connreq, cmd: string) {
        await this.getIndex();
        ....
    }

Javascript make函数在继续之前要等待另一个函数

3 个答案: