Within Angular, the Subscribe function is invoked after all other methods in the component have been executed. Consequently, this sequence of events often prevents me from effectively utilizing the response data

Question

Within Angular, the Subscribe function is invoked after all other methods in the component have been executed. Consequently, this sequence of events often prevents me from effectively utilizing the response data

Struggling with implementing await and async in TypeScript, especially as a beginner. Below is how I attempted to use them:

async refreshList(){
 await this.service.refreshList().subscribe(res => {
   console.log(res);
   this.service.todoListModel=res;
   });
}

Through debugging and console output, I discovered that the subscribe method's code executes last. I need help fixing the component code below:

import { Component, OnInit } from '@angular/core';
// more imports...

@Component({
  selector: 'todo',
  templateUrl: './todo.component.html',
  styleUrls: ['./todo.component.css'],
  providers: [TodoService],
  animations: [
    // animations...
  ]
})
export class TodoComponent implements OnInit {
  
  constructor(public service:TodoService) {
    this.refreshList(); 
    console.log(this.service.todoListModel);   
  }
  
  // other methods...
  
  public onTimeChange(t:any){
    // method implementation...
  }
  
  addTodo(input: HTMLInputElement){
    // method implementation...
  }
  
  removeTodo(i:number){
    // method implementation...
  }
}

Seeking assistance in resolving my issue. Any guidance on effectively using await and async would be greatly appreciated.

angular typescript async-await angular-httpclient

Answer 1

Answer №1

Many thanks for all your hard work, I finally grasped the concepts of await and async methods after working on the following code:

import { animateChild, group, query, stagger, transition, trigger, useAnimation } from '@angular/animations';
import { Component, OnInit } from '@angular/core';
import { groupBy } from '@progress/kendo-data-query';
import { moveDown, slideIn, slideOut } from '../animations';
import { TodoService } from '../todo.service';
import { lastValueFrom } from 'rxjs';

@Component({
  selector: 'todo',
  templateUrl: './todo.component.html',
  styleUrls: ['./todo.component.css'],
  providers: [TodoService],
  animations: [
    trigger('todoAnimations',[
      transition(':enter',[
        group([
          query('h1', [
            useAnimation(moveDown)
          ]),
          query('input', [
            useAnimation(moveDown)
          ]),
          query('@todoItem', [
            stagger(125, animateChild())
          ]),
        ])
      ])
    ]),
    trigger('todoItem', [
      transition(':enter', [
        useAnimation(slideIn)
      ]),
      transition(':leave',[
        useAnimation(slideOut)
      ])
    ])
  ]
})
export class TodoComponent implements OnInit {
  
  constructor(public service:TodoService) {
    this.refreshList(); 
    
  }
  
  ngOnInit(): void {
  }

  async refreshList(){
    const list$ = this.service.refreshList();
    this.service.todoListModel= await lastValueFrom(list$);
    console.log(this.service.todoListModel);
    this.service.todoListModel.forEach(element => {
      this.service.todos.push({item:element.itemName as string,due:(new Date(element.dueDate)),hour: (new Date(element.dueDate)).getHours()});
    });
    this.organizeTodosByHour();
}

  organizeTodosByHour(){
    if(!this.service.todos) return null;
      this.service.hourlyTodos=groupBy(this.service.todos,[{field: "hour"}]);
      console.log(JSON.stringify(this.service.hourlyTodos,null,2));
      return 0;
  }

  public onTimeChange(t:any){
    
    t.hour=t.due.getHours();

    this.organizeTodosByHour();
    console.log(this.service.todos,this.service.hourlyTodos);
    
  }

  addTodo(input: HTMLInputElement){
    this.service.todos=[{item:input.value, due: new Date(), hour:(new Date()).getHours()},...this.service.todos];
    input.value='';
    this.organizeTodosByHour();
  }

  removeTodo(i:number){
    this.service.todos.splice(i,1);
    this.organizeTodosByHour();
  }
}

Answer 2

Many thanks for all your hard work, I finally grasped the concepts of await and async methods after working on the following code:

import { animateChild, group, query, stagger, transition, trigger, useAnimation } from '@angular/animations';
import { Component, OnInit } from '@angular/core';
import { groupBy } from '@progress/kendo-data-query';
import { moveDown, slideIn, slideOut } from '../animations';
import { TodoService } from '../todo.service';
import { lastValueFrom } from 'rxjs';

@Component({
  selector: 'todo',
  templateUrl: './todo.component.html',
  styleUrls: ['./todo.component.css'],
  providers: [TodoService],
  animations: [
    trigger('todoAnimations',[
      transition(':enter',[
        group([
          query('h1', [
            useAnimation(moveDown)
          ]),
          query('input', [
            useAnimation(moveDown)
          ]),
          query('@todoItem', [
            stagger(125, animateChild())
          ]),
        ])
      ])
    ]),
    trigger('todoItem', [
      transition(':enter', [
        useAnimation(slideIn)
      ]),
      transition(':leave',[
        useAnimation(slideOut)
      ])
    ])
  ]
})
export class TodoComponent implements OnInit {
  
  constructor(public service:TodoService) {
    this.refreshList(); 
    
  }
  
  ngOnInit(): void {
  }

  async refreshList(){
    const list$ = this.service.refreshList();
    this.service.todoListModel= await lastValueFrom(list$);
    console.log(this.service.todoListModel);
    this.service.todoListModel.forEach(element => {
      this.service.todos.push({item:element.itemName as string,due:(new Date(element.dueDate)),hour: (new Date(element.dueDate)).getHours()});
    });
    this.organizeTodosByHour();
}

  organizeTodosByHour(){
    if(!this.service.todos) return null;
      this.service.hourlyTodos=groupBy(this.service.todos,[{field: "hour"}]);
      console.log(JSON.stringify(this.service.hourlyTodos,null,2));
      return 0;
  }

  public onTimeChange(t:any){
    
    t.hour=t.due.getHours();

    this.organizeTodosByHour();
    console.log(this.service.todos,this.service.hourlyTodos);
    
  }

  addTodo(input: HTMLInputElement){
    this.service.todos=[{item:input.value, due: new Date(), hour:(new Date()).getHours()},...this.service.todos];
    input.value='';
    this.organizeTodosByHour();
  }

  removeTodo(i:number){
    this.service.todos.splice(i,1);
    this.organizeTodosByHour();
  }
}

Answer 3

Answer №2

To implement async/await, it is recommended to convert observables to promises. Instead of the deprecated method toPromise, use lastValueFrom for better efficiency.

import { lastValueFrom } from 'rxjs';

constructor(public service:TodoService) {
   (async () => {
         await this.refreshList();
         console.log(this.service.todoListModel);
   })();
  }

async refreshList(){
      const list$ = this.service.refreshList();
      this.service.todoListModel= await lastValueFrom(list$);;
}

For specific cases, there are other utility observable functions available. Refer to this link for more information.

Answer 4

To implement async/await, it is recommended to convert observables to promises. Instead of the deprecated method toPromise, use lastValueFrom for better efficiency.

import { lastValueFrom } from 'rxjs';

constructor(public service:TodoService) {
   (async () => {
         await this.refreshList();
         console.log(this.service.todoListModel);
   })();
  }

async refreshList(){
      const list$ = this.service.refreshList();
      this.service.todoListModel= await lastValueFrom(list$);;
}

For specific cases, there are other utility observable functions available. Refer to this link for more information.

Answer 5

Answer №3

Instead of loading the list inside the constructor, consider loading it in a resolver so that the data is already present in the component from the start. Alternatively, if you prefer to load it within the constructor, you can convert the Observable to a Promise.

updateList(): void {
    this.service.taskListModel =
       await this.service.updateList().toPromise();
}

Answer 6

Instead of loading the list inside the constructor, consider loading it in a resolver so that the data is already present in the component from the start. Alternatively, if you prefer to load it within the constructor, you can convert the Observable to a Promise.

updateList(): void {
    this.service.taskListModel =
       await this.service.updateList().toPromise();
}

Within Angular, the Subscribe function is invoked after all other methods in the component have been executed. Consequently, this sequence of events often prevents me from effectively utilizing the response data

Answer №1

Answer №2

Answer №3

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