Using Angular 2's ngModel directive to bind a value passed in from an

Question

Using Angular 2's ngModel directive to bind a value passed in from an

Using [(ngModel)] in my child component with a string passed from the parent via @Input() is causing some issues.

Although the string is successfully passed from the parent to the child, any changes made to it within the child component do not reflect back to the parent's value.

I am confused about what might be missing or causing this problem.

Parent Component:

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [(value)]="name"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyValue';
  constructor() {

  }
}

Child Component:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>My custom input</p>
      <textarea [(ngModel)]="value"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;

  constructor() {

  }
}

A Plnkr example demonstrating the issue can be found here: https://plnkr.co/edit/jCF5kt73P38EFYUAZF6l

angular typescript angular2-forms

Answer 1

Answer №1

If you want to implement a feature that notifies about changes, consider adding an output element:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>Input Field:</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>()

  update(value) {
    this.valueChange.emit(value);
  }

  constructor() {

  }
}

Answer 2

If you want to implement a feature that notifies about changes, consider adding an output element:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>Input Field:</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>()

  update(value) {
    this.valueChange.emit(value);
  }

  constructor() {

  }
}

Answer 3

Answer №2

Indeed, the @Input directive operates in a singular direction. It allows for communication from parent to child by notifying the child component of any changes made by the parent. Conversely, the parent component remains oblivious to any alterations within the child component when exclusively utilizing @Input.

Answer 4

Indeed, the @Input directive operates in a singular direction. It allows for communication from parent to child by notifying the child component of any changes made by the parent. Conversely, the parent component remains oblivious to any alterations within the child component when exclusively utilizing @Input.

Answer 5

Answer №3

Building upon the response from @Günter Zöchbauer, I have made some changes to the app.ts file.

Here is the updated app.ts code:

// Main app component
import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {Child} from './child'
import {FormsModule} from "@angular/forms";

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [value]="name" (valueChange)="updateValue($event)"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyUpdatedValue';
  constructor() {

  }
  
  updateValue(value){
      this.name = value;
    }
}

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App, Child ],
  bootstrap: [ App ]
})
export class AppModule {}

And here is the Child component:

import {Component, Input, Output, EventEmitter} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
      <p>My customized input</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>();

  constructor() {

  }

  update(value) {
    this.valueChange.emit(value);
  }
}

Answer 6

Building upon the response from @Günter Zöchbauer, I have made some changes to the app.ts file.

Here is the updated app.ts code:

// Main app component
import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {Child} from './child'
import {FormsModule} from "@angular/forms";

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [value]="name" (valueChange)="updateValue($event)"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyUpdatedValue';
  constructor() {

  }
  
  updateValue(value){
      this.name = value;
    }
}

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App, Child ],
  bootstrap: [ App ]
})
export class AppModule {}

And here is the Child component:

import {Component, Input, Output, EventEmitter} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
      <p>My customized input</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>();

  constructor() {

  }

  update(value) {
    this.valueChange.emit(value);
  }
}

Using Angular 2's ngModel directive to bind a value passed in from an

Answer №1

Answer №2

Answer №3

Similar questions

Error message shows explicit Typescript type instead of using generic type name

The error message "NodeJS TypeError: Model is not a constructor" indicates that

Error occurred when trying to import an external module using an invalid hook call

Observable emitting value after execution of method

Error message: Unable to modify the 'cflags' property of object '#<Object>' in Angular CLI and node-gyp

Issues with setting default values for controls in Angular's reactive forms

The data in my MySQL table is not appearing on an Angular Material table when using Node.js

Local hosting of Angular 8 application with Universal and i18n integration encountered issues

Using TypeScript to automatically deduce the output type of a function by analyzing the recursive input type

How can I access a service without the need to import its provider module?

Is there a method to run code in the parent class right after the child constructor is called in two ES6 Parent-Child classes?

What is the best way to incorporate a class creation pattern in Typescript that allows one class to dynamically extend any other class based on certain conditions?

Ways to determine if a date matches today's date within a component template

Tips for extracting individual fields from a payload in Angular 8

Using the Ngclass function with a pair of objects

Extracting values from an *ngFor loop in Angular 8 - Here's how to do

Removing scrollbar from table in React using Material UI

Implementing dynamic progress bar updates in an Angular application using Bootstrap

Using React Testing Library with TypeScript revealed issues with ES6 modules causing test failures

A guide to resolving the error "Cannot read properties of undefined (reading 'length')" while implementing pagination with react, Material-UI, and TypeScript