While validating in my Angular application, I encountered an error stating that no index signature with a parameter of type 'string' was found on type 'AbstractControl[]'

While trying to validate my Angular application, I encountered the following error:

src/app/register/register.component.ts:45:39 - error TS7053: Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'AbstractControl[] | { [key: string]: AbstractControl; }'.
  No index signature with a parameter of type 'string' was found on type 'AbstractControl[] | { [key: string]: AbstractControl; }'.

45             return control?.value === control?.parent?.controls[matchTo].value ? null : {isMatching: true}
                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The error originates from this method:

matchValues(matchTo: string): ValidatorFn {

   return (control: AbstractControl) => {

        return control?.value === control?.parent?.controls[matchTo].value ? null : {isMatching: true}
       }
    

}

As a newbie in Angular and TypeScript, I am uncertain about how to resolve it. Any assistance or guidance would be greatly appreciated.

javascriptangulartypescript

Answer №1

You must specify the type of index that the object possesses. In this scenario, it is an index based on strings.

matchValues(matchTo: string): ValidatorFn {
    return (control: AbstractControl) => {
        return control.value === (control?.parent?.controls as { [key: string]: AbstractControl })[matchTo].value ? null : { isMatching: true };
    }
}

Answer №2

By simply using // @ts-ignore, I was able to disregard the specific line and now everything is running smoothly.

Answer №3

When looking at the index here, it is not a string but rather a number. Therefore, the solution is as follows:

 compareValues(compareTo: string): ValidatorFn {
    return (control: AbstractControl) => {
      const controls = control?.parent?.controls as { [key: string]: AbstractControl; };
      let compareToControl = null;
      if (controls) compareToControl = controls[compareTo];
      return control?.value === compareToControl?.value
        ? null : { isMatching: true }
    }
  }

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