Is it possible to extend DefaultValueAccessor?

Is it possible to extend DefaultValueAccessor?

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Is it possible to extend DefaultValueAccessor?
Tag : angular , By : orneka
Date : November 28 2020, 11:01 PM

it fixes the issue With some newer angular version it is possible to extend the DefaultValueAccessor and register the value accessor without any problems.

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How to extend a javascript object to include a method using _.extend or $.extend?

Tag : javascript , By : Matthew Steed
Date : March 29 2020, 07:55 AM
Any of those help For example using Underscore library, the following code works: , Remove the extra );
var myobject = {};
_.extend(myobject, { 
  method: function() {
    return 'demo'
  } // ); <-- remove this

Angular2 No provider for Renderer! (NgModel -> Token NgValueAccessor -> DefaultValueAccessor -> Renderer)

Tag : angular , By : Nickolas
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further I custom modal of customModal.ts in shlomiassaf/angular2-modal. Specific, i add a input contain ngModel, it imported FORM_DIRECTIVES and directives. , I see two possibilities:
    import {Component,Renderer,ElementRef} from 'angular2/core';

      selector: 'child',
      template: '<div></div>',
    export class ChildComponent {
      constructor(private _renderer: Renderer,
               private el: ElementRef) {
var otherResolved = Injector.resolve([
  provide(DialogRef, { useValue: dialogRef})
  provide(Renderer, { useValue: this.renderer})

Implement DefaultValueAccessor won't trigger "registerOnChange"

Tag : angular , By : glisignoli
Date : March 29 2020, 07:55 AM
Does that help You need to implement a custom ControlValueAccessor instead of extending an DefaultValueAccessor. https://github.com/angular/angular/issues/9146#issuecomment-241191899
To implement ControlValueAccessor you should provide NG_VALUE_ACCESSOR token for this directive. The simplest solution could look like this:
import { 
  Input, forwardRef, Renderer2, 
  Injector, ElementRef, Directive
} from '@angular/core'

import { ControlValueAccessor, NG_VALUE_ACCESSOR, NgControl } from '@angular/forms';

export const PREV_VAL_VALUE_ACCESSOR: any = {
  useExisting: forwardRef(() => PrevValDirective),
  multi: true

  selector: '[ngModel][prevVal]',
  host: {
    '(input)': 'handleInput($event.target.value)',
    '(blur)': 'onTouched()',
export class PrevValDirective implements ControlValueAccessor {
  @Input() prevVal: string;

  onChange = (_: any) => {};
  onTouched = () => {};

    private _renderer: Renderer2, 
    private _elementRef: ElementRef, 
    private _inj: Injector) {

  writeValue(value: any): void {
    const normalizedValue = value == null ? '' : value;
    this._renderer.setProperty(this._elementRef.nativeElement, 'value', normalizedValue);

  registerOnChange(fn: (_: any) => void): void {
    this.onChange = fn;

  registerOnTouched(fn: () => void): void {
    this.onTouched = fn;

  setDisabledState(isDisabled: boolean): void {
    this._renderer.setProperty(this._elementRef.nativeElement, 'disabled', isDisabled);

  handleInput(value: any): void {
    if (value === this.prevVal) {
      let model = this._inj.get(NgControl);  // get NgModel
      model.control.setValue(model.value);   // set previous value
let model = this._inj.get(NgControl);
<input type="text" [(ngModel)]="val" prevVal="false">

For custom form components, is it possible to use DefaultValueAccessor instead of ControlValueAccessor?

Tag : angular , By : yossi
Date : March 29 2020, 07:55 AM
it should still fix some issue One possible solution could be using ngDefaultControl attribute on your custom component:
<div [formGroup]="form">
    <jg-search formControlName="x" ngDefaultControl></jg-search>
  selector: 'jg-search',
  template: `
   <input [formControl]="ngControl.control">
export class MyInput {
  constructor(public ngControl: NgControl) {}

TypeError: Class constructor DefaultValueAccessor cannot be invoked without 'new'

Tag : angular , By : Val
Date : March 29 2020, 07:55 AM
should help you out I've resolved by making the class implements ControlValueAccessor instead of extends DefaultValueAccessor.
As a consequence of that, I also had to implement the missing methods, so I added the following:
import { ControlValueAccessor } from "@angular/forms";
// ...

export class MyClass implements ControlValueAccessor {

  // ...

  onChange = (_: any) => {};
  onTouched = () => {};

  // ...

  registerOnChange(fn: (_: any) => void): void { this.onChange = fn; }
  registerOnTouched(fn: () => void): void { this.onTouched = fn; }

  setDisabledState(isDisabled: boolean): void {
    this._renderer.setProperty(this._elementRef.nativeElement, 'disabled', isDisabled);
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