Keep an ear out for updates on object changes in Angular

Question

Keep an ear out for updates on object changes in Angular

One of my challenges involves a form that directly updates an object in the following manner:

component.html

<input type="text" [(ngModel)]="user.name" />
<input type="text" [(ngModel)]="user.surname" />
<input type="text" [(ngModel)]="user.age" />

component.ts

user = {
  name: null,
  surname: null,
  age: null
}

Within my component.html, there is a save button implemented in a child component.

<app-save-btn [user]="user"></app-save-btn>

In the app-save-btn component, I am utilizing OnChanges to detect changes.

@Input() user: User;

userForCompare: User;

ngOnChanges() {
  if (!this.userForCompare) {
    this.userForCompare = {...this.user};
  }
  console.log(this.userForCompare, this.user);
}

My issue arises when I update additional fields beyond the initial ones - I do not receive updated change information.

While I understand that I could create individual variables for each field, as I have approximately 30 fields, I would prefer to keep my current implementation relatively unchanged...

Any assistance or guidance on this matter would be greatly appreciated.

javascript angular typescript

Answer 1

Answer №1

@Input property will only activate the ngOnChanges function if the Input object is modified.

In this scenario, each input field modifies a different property within the same user object. Even though the child properties (name, surname, and age) of the user object are changed, the ngOnChanges function will not be triggered because the @Input always points to the same object.

As a solution, you need to assign a completely new user object to this.user in the component.ts file whenever any input field is altered.

I hope this explanation clarifies things for you!

Answer 2

@Input property will only activate the ngOnChanges function if the Input object is modified.

In this scenario, each input field modifies a different property within the same user object. Even though the child properties (name, surname, and age) of the user object are changed, the ngOnChanges function will not be triggered because the @Input always points to the same object.

As a solution, you need to assign a completely new user object to this.user in the component.ts file whenever any input field is altered.

I hope this explanation clarifies things for you!

Answer 3

Answer №2

If you want to efficiently manipulate your form fields, I recommend creating a FormGroup using Reactive Forms. By utilizing FormBuilder.group(), you can easily create a form that includes properties of the User object. This way, you only need to pass form.value to your child component.

Reactive forms maintain the purity of the data model by treating it as an immutable data structure. Whenever changes are made to the form, the FormControl instance does not update the existing data model; instead, it returns a new state (a new data model).

You can see a working example on StackBlitz with the following code:
https://stackblitz.com/edit/angular-stackoverflow-60424523

example.component.html

<form [formGroup]="form">
  <input [formControlName]="'name'" />
  <input [formControlName]="'surname'" />
  <input [formControlName]="'age'" />
</form>
<app-save-btn [user]="form.value"></app-save-btn>

example.component.ts

import { Component, OnInit} from '@angular/core';
import { FormBuilder, FormGroup} from '@angular/forms';

@Component({ ... })
export class AppComponent implements OnInit {

  form: FormGroup;

  user: User = {
    name: 'Initial name',
    surname: 'Initial surname',
    age: 99
  };

  constructor(
    private formBuilder: FormBuilder,
  ) { }

  ngOnInit() {
    this.form = this.formBuilder.group(this.user);
  }
}

Answer 4

If you want to efficiently manipulate your form fields, I recommend creating a FormGroup using Reactive Forms. By utilizing FormBuilder.group(), you can easily create a form that includes properties of the User object. This way, you only need to pass form.value to your child component.

Reactive forms maintain the purity of the data model by treating it as an immutable data structure. Whenever changes are made to the form, the FormControl instance does not update the existing data model; instead, it returns a new state (a new data model).

You can see a working example on StackBlitz with the following code:
https://stackblitz.com/edit/angular-stackoverflow-60424523

example.component.html

<form [formGroup]="form">
  <input [formControlName]="'name'" />
  <input [formControlName]="'surname'" />
  <input [formControlName]="'age'" />
</form>
<app-save-btn [user]="form.value"></app-save-btn>

example.component.ts

import { Component, OnInit} from '@angular/core';
import { FormBuilder, FormGroup} from '@angular/forms';

@Component({ ... })
export class AppComponent implements OnInit {

  form: FormGroup;

  user: User = {
    name: 'Initial name',
    surname: 'Initial surname',
    age: 99
  };

  constructor(
    private formBuilder: FormBuilder,
  ) { }

  ngOnInit() {
    this.form = this.formBuilder.group(this.user);
  }
}

Keep an ear out for updates on object changes in Angular

Answer №1

Answer №2

Similar questions

Scrolling to specific ID scrolls only in a downward direction

When utilizing Angular CDK virtual scroller, an error occurs stating that @angular/core/core does not have an exported member 'ɵɵFactoryDeclaration'. Can anyone explain why this is happening

Understanding the process of reading cookies on the Angular2 side that have been set by the C# server

Ways to Implement an Origin's First-Party Cookies While Using it as a Third-Party

Guide on comparing an object against an array and retrieving a specific output

What is the best way to divide a string into an array containing both linked and non-linked elements?

Incorporating a delay into looped HTTP requests while effectively utilizing Promise.all to track their completion

What is the method to retrieve values passed to the next() function in Node.js?

Creating a Star Rating system with jQuery using a dropdown menu for multiple selections

Guide on converting arrays and sending this information in Node.js

Struggling to set up a Jest testing module for a NestJs service. Encountering an issue where Nest is unable to resolve dependencies of the UsersService, specifically the Config

Loading website with continuous HTML5 video playback

What could be causing the .hover function to malfunction and how can I make it so that the .hover function only applies within the corner radius area?

Angular 4's Panel Window: A User-Friendly Interface

How can I pass an argument to Node within a package.json script instead of the script itself?

Managing various encoding methods when retrieving the XML data feed

How can I select the specific element within a class when a particular checkbox is selected?

Troubleshooting React: Child Component Fails to Render

Establish the state as the result of a function

Using Node.js to Merge the Responses of Two Results