How to extend FormControl functionality via prototype?-CodePudding

I want all objects of the FormControl type to have the observable (or event emitter) field (e.g. onMarkAsDirty) which will be triggered on markAsDirty method call. I tried to implement this by extending FormControl prototype, but it is too hard for me. Can you help me please and write some sketches?

CodePudding user response：

Extends a class is easy. You has the code of the FormControl (Really of AbstractControl) in github

So you can define

export class FormControlExtends extends FormControl {
  markAsDirty(opts: { onlySelf?: boolean } = {}): void {
    (this as { pristine: boolean }).pristine = false;
    
    if (this['_parent'] && !opts.onlySelf) {
      this['_parent'].markAsDirty(opts);
    }
    //make some more
    console.log('say hello');
  }
}

See that to access to a private variable (in this case "_parent") use square bracket, e.g. not this._parent else this['_parent']

And you can use as

control=new FormControlExtends(null)

a stackblitz