Angular - Error: Expression has been modified after it was already checked

I'm at my wit's end trying to figure this out. I've searched high and low, but I just can't seem to understand why this error persists.

My code looks something like this:

parent.html

<child-1 [(type)]="type"></child-1>

parent.ts

type = 0;
getTypeToOtherthings() { 
    console.log(type);
}

child-1.html

<child-2 [(type)]="type">

child-1.ts // acting as a connection between parent and child-2

_type: number;
@Input() set type(val: number) {
  this.typeChange.emit(val);
  this._type= val;
}
get type() {
  return this._type;
}
@Output() typeChange: EventEmitter<number> = new EventEmitter<number>();

child-2.html

(some HTML)

child-2.ts

_type: number;
@Input() set type(val: number) {
  this.typeChange.emit(val);
  this._type= val;
}
get type() {
  return this._type;
}
@Output() typeChange: EventEmitter<number> = new EventEmitter<number>();

/*Trying to change the Type variable in child-2, attempted in ngOnInit (and various other lifecycle hooks with no success using Promise, ChangeDetectorRef, etc.
Everything seems fine, yet the error still persists)*/
ngOnInit() {
    this.type = 2;
}

At this point, I'm nearly ready to throw in the towel.

Answer №1

If you encounter this problem and are able to pinpoint the issue, a quick workaround is to execute it within a setTimeout function like so:

setTimeout(()=> this.markersEventsType = 2;)

Alternatively, there may be a more appropriate solution available. Have you considered setting the eventType in the constructor? If the change is coming from a service, perhaps utilizing the async pipe could help.

Answer №2

If you're encountering an issue within your app, it may be due to a discrepancy between the model and view being modified. Angular's devMode adds extra update checks to ensure that any changes in the model are reflected in the view.

The error message indicates that none of these checks were able to detect a change in the model. One potential solution is to utilize ChangeDetectorRef. By calling detectChanges(), you can inform your app of any modifications in the model, prompting the view to update accordingly.

Furthermore, I highly recommend exploring change detection strategies as they can enhance code clarity and optimize app performance by enforcing the use of ChangeDetection.

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