Angular2 Component @Input two way binding

78
votes

I have a data driven Angular application. I have a toggle component which I pass in a toggled state. My issue is that the two way data binding does not seem to work unless i pass in the toggle boolean as an object. Is there a way to get this to work without using an EventEmitter or passing the variable in as an object. This is to be a reusable component and the application is heavily data driven so passing the value in as an object in not an option. My code is....

toggle.html

<input type="checkbox" [(ngModel)]="toggled" [id]="toggleId" name="check"/>

toggle.component.ts

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

@Component({
  moduleId: module.id,
  selector: 'toggle-switch',
  templateUrl: 'toggle-switch.component.html',
  styleUrls: ['toggle-switch.component.css']
})

export class ToggleSwitchComponent {

  @Input() toggleId: string;
  @Input() toggled: boolean;

}

parent.component.html

<toggle-switch toggleId="toggle-1" [(toggled)]="nongenericObject.toggled"></toggle-switch>
2
angulartypescriptdata-bindingcomponentsdecorator
I'd like to stress the importance of mitch's comment on this. To make two-way-binding with a parent component's var work, the @Output decorated EventEmitter has to be named as the corresponding @Input with a Change suffix at the end as in: @Input() toggled: boolean; @Output() toggledChange: EventEmitter<boolean> = new EventEmitter<boolean>(); – Andreas

2 Answers

139
votes

For [(toggled)]="..." to work you need 

  @Input() toggled: boolean;
  @Output() toggledChange: EventEmitter<boolean> = new EventEmitter<boolean>();

  changeValue() {
    this.toggled = !(this.toggled); 
    this.toggledChange.emit(this.toggled);
  }

See also Two-way binding

[UPDATE] - 25 June 2019
From @Mitch's comment below:
It's worth noting that the @Output name must be the same as the @Input name, but with Change on the end. You can't call it onToggle or something. It's a syntax convention.

13
votes

Although the question has more than 2 years old I want to contribute my 5 cents...

It isn't a problem about Angular, its about how Javascript works... Simple variables (number, string, boolean, etc) are passed by value whereas complex ones (objects, arrays) are passed by reference:

You can read more about this in Kyle Simpson´s series You dont know js:

https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch2.md#value-vs-reference

So, you can use an @Input() object variable to share scope between components without need to use emitters, observers and whatever similar.

// In toggle component you define your Input as an config object
@Input() vm: Object = {};

// In the Component that uses toggle componet you pass an object where you define all needed needed variables as properties from that object:
config: Object = {
    model: 'whateverValue',
    id: 'whateverId'
};

<input type="checkbox" [vm]="config" name="check"/>

This way you can modify all object properties and you get same value in both components because they share same reference.