Angular is patiently waiting for the initial function to activate

Question

Angular is patiently waiting for the initial function to activate

I have a situation where I need to wait for the results of my first function before executing the second one.

code

First function

getUser() {
    this.authService.user().subscribe(
        user => {
        this.user = user;
        console.log('current user 1: ', user);
        console.log('current user 2: ', this.user);
        }
    );
}

async ngOnInit() {
    this.socket.fromEvent('message').subscribe(async (message: any) => {
        if(this.user === undefined) {
            // call the first function
            this.getUser();
            // this console log will fire before the function finishes, resulting in 'undefined'
            console.log('this user: ', this.user);
        } else {
            //....
        }
    }
}

I need to delay my console call until this.getUser(); is completed. What is the best way to achieve this?

javascript angular typescript ionic-framework

Answer 1

Answer №1

If you want to transform your getUser() method into a promise, you can do it like this:

getUser():Promise<any>{
   return new Promise((resolve,reject) =>{
     this.authService.user().toPromise().then(user => {
       this.user = user;
       console.log('current user 1: ', user);
       console.log('current user 2: ', this.user);
       resolve(user);
     }).catch(err=> reject(err));
   });
}

Then, in your ngOnInit():

async ngOnInit(){
  this.socket.fromEvent('message').subscribe(async (message: any) => {
    if(this.user === undefined) {
        // first function called
        await this.getUser().then(user=>{
           console.log('this user: ', user);
        });
    }
  });
}

Additionally, consider using toPromise() when you only need data from an observer once. Subscribing to an observer without unsubscribing can result in memory leaks.

Answer 2

If you want to transform your getUser() method into a promise, you can do it like this:

getUser():Promise<any>{
   return new Promise((resolve,reject) =>{
     this.authService.user().toPromise().then(user => {
       this.user = user;
       console.log('current user 1: ', user);
       console.log('current user 2: ', this.user);
       resolve(user);
     }).catch(err=> reject(err));
   });
}

Then, in your ngOnInit():

async ngOnInit(){
  this.socket.fromEvent('message').subscribe(async (message: any) => {
    if(this.user === undefined) {
        // first function called
        await this.getUser().then(user=>{
           console.log('this user: ', user);
        });
    }
  });
}

Additionally, consider using toPromise() when you only need data from an observer once. Subscribing to an observer without unsubscribing can result in memory leaks.

Answer 3

Answer №2

When utilizing combineLatest

combineLatest(this.authService.user(), this.socket.fromEvent('message'))
  .subscribe(([user, message]) => {
    // You can access both the message and user simultaneously
  });

Answer 4

When utilizing combineLatest

combineLatest(this.authService.user(), this.socket.fromEvent('message'))
  .subscribe(([user, message]) => {
    // You can access both the message and user simultaneously
  });

Answer 5

Answer №3

To resolve the issue, make sure to include 'await' in your code as shown below:

async ngOnInit() {
this.socket.fromEvent('message').subscribe(async (message: any) => {
    if(this.user === undefined) {
        // first function called
        await this.getUser();
        // The console log will fire before the function finishes, returning 'undefined'
        console.log('this user: ', this.user);
    } else {
        //....
    }
}}

Answer 6

To resolve the issue, make sure to include 'await' in your code as shown below:

async ngOnInit() {
this.socket.fromEvent('message').subscribe(async (message: any) => {
    if(this.user === undefined) {
        // first function called
        await this.getUser();
        // The console log will fire before the function finishes, returning 'undefined'
        console.log('this user: ', this.user);
    } else {
        //....
    }
}}

Angular is patiently waiting for the initial function to activate

code

Answer №1

Answer №2

Answer №3

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