Troubleshooting issues with setting errors on a FormGroup instance in Angular Reactive Forms are proving to be more challenging

Currently I am working with Angular 4.4.3 reactive forms to create custom validation for a group of controls within a form. As per the documentation on AbstractControl.setErrors, this method updates the errors property of the AbstractControl that it's called upon, and also updates the status of its parent. However, it does not update the parent's errors property. My goal was to set the errors property on a FormGroup instance by using the inherited setErrors method from FormGroup. Surprisingly, it did not update the errors as expected.

Below is a snippet of my code: When trying this approach on FormControl instances, it successfully updates their errors along with their parents' validity status (although the parents' errors remain unaffected):

let myFormGroup 
    = this._formBuilder
          .group({
                   ctrl1: [null],
                   ctrl2: [null]
                 }, 
                 {
                   validator: (fg: FormGroup) => {
                                   let ctrl1 = fg.get('ctrl1'),
                                       ctrl2 = fg.get('ctrl2'),
                                       ctrl1Empty = !ctrl1.value,
                                       ctrl2Empty = !ctrl2.value;

                                       //Successfully sets ctrl1.errors and fg.status, but not fg.errors 
                                       if (ctrl1empty)
                                         ctrl1.setErrors({ctrl1required: true});
                                       //Successfully sets ctrl2.errors and fg.status, but not fg.errors 
                                       if (ctrl2Empty)
                                         ctrl2.setErrors({ctrl2required: true});
                                       //Doesn't work, doesn't update fg.errors
                                       if (ctrl1Empty && ctrl2Empty)
                                         fg.setErrors({required: true});
                              }
                 })

Any insights on why this might be happening?

Answer №1

After receiving confirmation from @incognito, I was able to pinpoint the issue upon closer examination.

Although setErrors does indeed set the errors property of the form group instance, the custom validator mentioned in my initial query did not explicitly return a value (i.e., a falsey undefined value). Upon delving into the reactive forms module code within Angular, I came across this method. In this method, errors raised by various validators are merged at this line, where it checks if errors (undefined in my code snippet) are not equal to null. This particular condition, when evaluated in its es5 version, results in false, culminating in a null outcome and hence disregarding the contents of the errors property defined in the code. The valuable lesson learned here is: always ensure custom validators return a value, even if subsequent nested FormGroup instances have their own customized logic for error handling.

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