Modifying an @Input element within a component does not result in any changes being reflected in the parent component

Question

Modifying an @Input element within a component does not result in any changes being reflected in the parent component

Here is the scenario with my component:

@Component({
    selector: 'child'
})
export class ChildComponent {
    @Input() childObject: ChildObject;

    changeObject(newObject: ChildObject){
        childObject = newObject;
    }
}

After calling changeObject, the changes are reflected in my ChildComponent, but the parent component (ParentComponent) which includes the ChildComponent does not update accordingly.

For instance, if I have {{parent.childObject.name}} in the template of my ParentComponent, this value remains unchanged.

I attempted to use

childObject = JSON.parse(JSON.stringify(newObject));

without success. It seems to be an issue related to object reference modification. As a solution, I created a method called copy(newObject: ChildObject) in my ChildObject class to copy the properties one by one. However, when I call it within the changeObject method, I encounter the following error:

ERROR TypeError: _this.childObject.copy is not a function.

Update: Definition of ChildObject class

export class ChildObject {
  constructor(
    public name: string // , ...
  ) { }

  copy(childObject: ChildObject) {
    this.name = childObject.name;
    // ...
  }
}

javascript angular typescript

Answer 1

Answer №1

It is recommended to utilize the service or @Output for effective communication between components. If there will be only this level of communication, I suggest using @Output in this scenario.

@Component({
    selector: 'child'
})
export class ChildComponent {
    @Input() childObject: ChildObject;
    @Output() onChildObjectChange = new EventEmitter<ChildObject>();
    changeObject(newObject: ChildObject){
        childObject = newObject;
        this.onChildObjectChange.emit(newObject);
    }
}

Parent component Html

<child (onChildObjectChange)="updateObject($event)"></child>

ts

updateObject(newObject: ChildObject) {
  childObject = newObject
}

Answer 2

It is recommended to utilize the service or @Output for effective communication between components. If there will be only this level of communication, I suggest using @Output in this scenario.

@Component({
    selector: 'child'
})
export class ChildComponent {
    @Input() childObject: ChildObject;
    @Output() onChildObjectChange = new EventEmitter<ChildObject>();
    changeObject(newObject: ChildObject){
        childObject = newObject;
        this.onChildObjectChange.emit(newObject);
    }
}

Parent component Html

<child (onChildObjectChange)="updateObject($event)"></child>

ts

updateObject(newObject: ChildObject) {
  childObject = newObject
}

Answer 3

Answer №2

UPDATE: Replacing the original object reference with a direct assignment will not be effective

this.childObject = newObject; // This method will not yield results

Instead, making updates to an existing object should produce the desired outcome

this.childObject.someProperty = newObject; // this approach should work

Object.assign(this.childObject, newObject);  // this method should work as it merges the objects

Since objects are passed as references while passing inputs, it should work fine. The issue lies in the code you provided where the childObject should be referenced as this.childObject

@Component({
    selector: 'child'
})
export class ChildComponent {
    @Input() childObject: ChildObject;

    changeObject(newObject: ChildObject){
        this.childObject = newObject;
    }
}

This method should function correctly, although there may be cleaner ways to achieve the same result.

Answer 4

UPDATE: Replacing the original object reference with a direct assignment will not be effective

this.childObject = newObject; // This method will not yield results

Instead, making updates to an existing object should produce the desired outcome

this.childObject.someProperty = newObject; // this approach should work

Object.assign(this.childObject, newObject);  // this method should work as it merges the objects

Since objects are passed as references while passing inputs, it should work fine. The issue lies in the code you provided where the childObject should be referenced as this.childObject

@Component({
    selector: 'child'
})
export class ChildComponent {
    @Input() childObject: ChildObject;

    changeObject(newObject: ChildObject){
        this.childObject = newObject;
    }
}

This method should function correctly, although there may be cleaner ways to achieve the same result.

Answer 5

Answer №3

To change the value, you can consider adding ChangeDetectionStrategy.OnPush to your child component:

@Component({
    selector: 'child',
    changeDetection: ChangeDetectionStrategy.OnPush
})
export class ChildComponent {
    @Input() childObject: ChildObject;

    changeObject(newObject: ChildObject){
        childObject = newObject;
    }
}

By doing this, your object will be updated whenever there is an event triggered on the child component. Both the child and parent components' changeDetection will occur, causing the update of your object.

I hope this aligns with what you were looking for - Happy coding!!

Answer 6

To change the value, you can consider adding ChangeDetectionStrategy.OnPush to your child component:

@Component({
    selector: 'child',
    changeDetection: ChangeDetectionStrategy.OnPush
})
export class ChildComponent {
    @Input() childObject: ChildObject;

    changeObject(newObject: ChildObject){
        childObject = newObject;
    }
}

By doing this, your object will be updated whenever there is an event triggered on the child component. Both the child and parent components' changeDetection will occur, causing the update of your object.

I hope this aligns with what you were looking for - Happy coding!!

Modifying an @Input element within a component does not result in any changes being reflected in the parent component

Answer №1

Answer №2

Answer №3

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