FormGroup reset() throws if a control is removed from valueChanges subscription

🐞 bug report

Affected Package

The issue is caused by package @angular/forms

Is this a regression?

not sure

Description

During OnChanges, we reset a form group. This causes the valueChanges to fire which causes a control to be remove from the group, via a subscription to the valueChanges event. The issue is that this control is still part of the form groups dictionary of named control but the value is null.

🔬 Minimal Reproduction

The below code for the reset function calls control.reset as it iterates each control. Since the control is null, there is no reset function.

• the work around was to set the emitEvent option to false, but that causes other issues since we are listening for other valueChanges events… so we have to work around those. FormGroup.prototype.reset = function (value, options) { if (value === void 0) { value = {}; } if (options === void 0) { options = {}; } this._forEachChild(function (control, name) { control.reset(value[name], { onlySelf: true, emitEvent: options.emitEvent }); }); this.updateValueAndValidity(options); this._updatePristine(options); this._updateTouched(options); };

https://stackblitz.com/edit/angular-uiibu2

🔥 Exception or Error

TypeError: Cannot read property 'reset' of undefined

🌍 Your Environment

Angular Version:

6.1

Anything else relevant?

[ShiftySituation]

@kara I ran into the issue again today and created a repo while it was still fresh in my mind.

https://stackblitz.com/edit/angular-uiibu2

simply type 1 in the input box and hit save. when you type 1, it will cause the value change to fire which adds another control to the form group via the subscription set up in ngOnInit. When you hit save, it resets the formGroup, causing the value change to fire again which removes the control. This creates the error, “TypeError: Cannot read property ‘reset’ of undefined” since it is trying to reset each control of the formGroup even though the control has been removed.

[ShiftySituation]

I’ll test this again and provide a repro tomorrow. been on vacation for the past month 😉