ValueChanges on FormControl triggers when Form.enable, even with emitEvent: false

Question

With Angular (4.x) I use ReactiveForms and I've subscribed to valueChanges on my FormControl ("input") like so:

export class App {
  version:string;
  formControl = new FormControl('default', []);
  form = this.fb.group({
        input: this.formControl,
        input2: ('',[])
    });

  constructor(private fb: FormBuilder) {
    this.version = `Angular v${VERSION.full}`
  }

  ngOnInit() {
    this.formControl.valueChanges.subscribe(value => doSomething(value));
  }

So now I can react on changes on the value of my FormControl, but I of course fill the values of the form from somewhere to start with, so I use form.patchValue(data) to do so.

Since this is not a userchange, I don't want to react on it, so add the flag emitEvent: false, like: this.form.patchValue(data, {emitEvent: false}).

Which works as expected.

Now I have some logic that when the form is loading, I set the whole form to disabled, this.form.disable({ emitEvent: false }), and when finished loading it sets the whole form to enabled again: this.form.disable({ emitEvent: false })

But I also have logic that depending on different flags sets the FormControl to enabled/disabled: this.formControl.enable( {emitEvent: false});

---

The problem I'm now see is that when the Form, changes status, it triggers the FormControl.valueChanges, even though I provide the emitEvent: false flag.

Is this the expected behavior, or a bug? I expected no event to be triggered at all when providing the flag?

I've made a plunk where this can be tested here: https://plnkr.co/edit/RgyDItYtEfzlLVB6P5f3?p=preview

Answer 1

both disable() and enable() functions (code source):

/**
 * Disables the control. This means the control will be exempt from validation checks and
 * excluded from the aggregate value of any parent. Its status is `DISABLED`.
 *
 * If the control has children, all children will be disabled to maintain the model.
 * @param {?=} opts
 * @return {?}
 */
AbstractControl.prototype.disable = function (opts) {
    if (opts === void 0) { opts = {}; }
    this._status = DISABLED;
    this._errors = null;
    this._forEachChild(function (control) { control.disable({ onlySelf: true }); });
    this._updateValue();
    if (opts.emitEvent !== false) {
        this._valueChanges.emit(this._value);
        this._statusChanges.emit(this._status);
    }
    this._updateAncestors(!!opts.onlySelf);
    this._onDisabledChange.forEach(function (changeFn) { return changeFn(true); });
};
/**
 * Enables the control. This means the control will be included in validation checks and
 * the aggregate value of its parent. Its status is re-calculated based on its value and
 * its validators.
 *
 * If the control has children, all children will be enabled.
 * @param {?=} opts
 * @return {?}
 */
AbstractControl.prototype.enable = function (opts) {
    if (opts === void 0) { opts = {}; }
    this._status = VALID;
    this._forEachChild(function (control) { control.enable({ onlySelf: true }); });
    this.updateValueAndValidity({ onlySelf: true, emitEvent: opts.emitEvent });
    this._updateAncestors(!!opts.onlySelf);
    this._onDisabledChange.forEach(function (changeFn) { return changeFn(false); });
};

have call to:

this._updateAncestors(!!opts.onlySelf);

which calls its parent's updateValueAndValidity() function without emitEvent flag, which then calls

this._valueChanges.emit(this._value);

this triggers valueChanges emitter of the form and you see in console:

Form.valueChanges: Object { input2: null }

this is triggered by form and not by the default input field controller. In order to stop ancestor updating, we just need to provide additional flag - onlySelf: true, which tells to update only its self and not ancestors. So, in each call to disable() or enable() functions where you do not want to update ancestors add this flag:

disable(){
  this.form.disable({
    onlySelf: true, 
    emitEvent: false
  });
}

disableWEvent(){
  this.form.disable({
    onlySelf: true
  });
}

enable(){
  this.form.enable({
    onlySelf: true, 
    emitEvent: false
  });
}

enableWEvent(){
  this.form.enable({
    onlySelf: true
  });
}

disableCtrl(){
  this.formControl.disable({
    onlySelf: true, 
    emitEvent: false
  });
}

disableCtrlWEvent(){
  this.formControl.disable({
    onlySelf: true
  });
}

enableCtrl(){
  this.formControl.enable({
    onlySelf: true, 
    emitEvent: false
  });
}

enableCtrlWEvent(){
  this.formControl.enable({
    onlySelf: true
  });
}

this will solve the problem for leaf formControls (controls without children), but this line

this._forEachChild(function (control) { control.disable({ onlySelf: true }); });

will call disable (or enable) function without passed emitEvent: false. It looks like angular bug, so, as workaround, we can override these two functions. First import AbstractControl:

import {ReactiveFormsModule, FormBuilder, FormControl, Validators, AbstractControl} from '@angular/forms'

than override both functions:

// OVERRIDE disable and enable methods
// https://github.com/angular/angular/issues/12366
// https://github.com/angular/angular/blob/c59c390cdcd825cca67a422bc8738f7cd9ad42c5/packages/forms/src/model.ts#L318
AbstractControl.prototype.disable = function (opts) {
  if (opts === void 0) { opts = {}; }
  this._status = 'DISABLED';
  this._errors = null;
  this._forEachChild(function (control) { 
    control.disable(Object.assign(opts, {onlySelf: true})); 
  });
  this._updateValue();
  if (opts.emitEvent !== false) {
      this._valueChanges.emit(this._value);
      this._statusChanges.emit(this._status);
  }
  this._updateAncestors(!!opts.onlySelf);
  this._onDisabledChange.forEach(function (changeFn) { return changeFn(true); });
};
AbstractControl.prototype.enable = function (opts) {
  if (opts === void 0) { opts = {}; }
  this._status = 'VALID';
  this._forEachChild(function (control) { 
    control.enable(Object.assign(opts, {onlySelf: true})); 
  });
  this.updateValueAndValidity({ onlySelf: true, emitEvent: opts.emitEvent });
  this._updateAncestors(!!opts.onlySelf);
  this._onDisabledChange.forEach(function (changeFn) { return changeFn(false); });
};

updated plunker: https://plnkr.co/edit/IIaByz4GlBREj2X9EKvx?p=preview