interface ControlValueAccessor { 
 writeValue(obj: any): void
 registerOnChange(fn: any): void
 registerOnTouched(fn: any): void
}

import { ControlValueAccessor } from '@angular/forms/src/directives';
import { Component, forwardRef, Input } from '@angular/core';
import { NG_VALUE_ACCESSOR } from '@angular/forms';

@Component({
 selector: 'custom-input',
 template: `<input [(ngModel)]="value"/>`,
 providers: [
  {
   provide: NG_VALUE_ACCESSOR,
   useExisting: forwardRef(() => UnionInputComponent),
   multi: true
  }
 ]
})
export class CustomInputComponent implements ControlValueAccessor {
 constructor() { }
 private innerValue: any = '';
 private onTouchedCallback: () => void = function () { };
 private onChangeCallback: (_: any) => void = function () { };

 get value(): any {
  return this.innerValue;
 }
 set value(v: any) {
  if (v !== this.innerValue) {
   this.innerValue = v;
   this.onChangeCallback(v);
  }
 }
 /**
  * model view -> view value
  */
 writeValue(value: any) {
  if (value !== this.innerValue) {
   this.innerValue = value;
  }
 }
 /**
  * view value ->model value
  */
 registerOnChange(fn: any) {
  this.onChangeCallback = fn;
 }
 registerOnTouched(fn: any) {
  this.onTouchedCallback = fn;
 }
}

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

@Component({
 selector: 'custom-input',
 template: `<input [(ngModel)]="innerValue"/>`,
})
export class CustomInputComponent {
 innerValue;

 @Input()
 get twoWayModel() {
  return this.innerValue;
 }
 set twoWayModel(val) {
  this.innerValue = val;
  this.twoWayModelChange.emit(this.innerValue);
 }
 @Output() twoWayModelChange: EventEmitter<string> = new EventEmitter</string><string>();
}

import { Input, Output } from '@angular/core';
import { Component, forwardRef, Input } from '@angular/core';
@Component({
 selector: 'custom-input',
 template: `<custom -input [(twoWayModel)]="inputValue" (twoWayModelChange)="onInputValueChange($event)"></custom>`
})
export class abcComponent {
 inputValue;
 onInputValueChange(val) {
  console.log(val);
  console.log(val === this.inputValue); // true
 }
}