A TypeScript function containing dual return statements

Question

A TypeScript function containing dual return statements

Consider the following code snippet:

export function forbiddenNameValidator(nameRe: RegExp): ValidatorFn {
  return (control: AbstractControl): { [key: string]: any } | null => {
    const forbidden = nameRe.test(control.value)
    return forbidden ? { forbiddenName: { value: control.value } } : null
  }
}

Source: https://angular.io/guide/form-validation#custom-validators

This function acts as a factory that accepts a regular expression to identify a specific prohibited name and generates a validator function.

The function returns a ValidatorFn, which in turn can return an error message or null.
So, what will actually be returned when using this function?

angular typescript

Answer 1

Answer №1

Consider using a reactive form as an example for adding validation. By including Validators.propertyname, you can specify the expected type of the second argument as either a ValidatorFn or ValidatorFn[] in formcontrol.

To implement custom validation in the first return, you need to include a ValidatorFn return value within the array.

The second return pertains to the logic executed when the validation process is triggered. This may involve running additional logic inside your ValidatorFn, such as a callback or promise.

new FormControl(this.hero.name, [
      Validators.required, --

      forbiddenNameValidator(/bob/i) // <-- Custom validator implementation.
    ]),

Include validation in the array -->   return (control: AbstractControl): {[key: string]: any} | null => {
                               const forbidden = nameRe.test(control.value);
Execute logic during validation -->   return forbidden ? {'forbiddenName': {value: control.value}} : null;
                             };

Think of built-in validations like Validators.required, which are included in the validation array and utilized when the form value changes. The logic written within this function is then executed, returning a value based on the specific use case or setting an error variable.

Answer 2

Consider using a reactive form as an example for adding validation. By including Validators.propertyname, you can specify the expected type of the second argument as either a ValidatorFn or ValidatorFn[] in formcontrol.

To implement custom validation in the first return, you need to include a ValidatorFn return value within the array.

The second return pertains to the logic executed when the validation process is triggered. This may involve running additional logic inside your ValidatorFn, such as a callback or promise.

new FormControl(this.hero.name, [
      Validators.required, --

      forbiddenNameValidator(/bob/i) // <-- Custom validator implementation.
    ]),

Include validation in the array -->   return (control: AbstractControl): {[key: string]: any} | null => {
                               const forbidden = nameRe.test(control.value);
Execute logic during validation -->   return forbidden ? {'forbiddenName': {value: control.value}} : null;
                             };

Think of built-in validations like Validators.required, which are included in the validation array and utilized when the form value changes. The logic written within this function is then executed, returning a value based on the specific use case or setting an error variable.

Answer 3

Answer №2

Here is a custom function that generates a ValidatorFn, which can either return an error message or null.
What do you think the final output will be?

You mentioned that forbiddenNameValidator produces a function that belongs to the ValidatorFn type.

Answer 4

Here is a custom function that generates a ValidatorFn, which can either return an error message or null.
What do you think the final output will be?

You mentioned that forbiddenNameValidator produces a function that belongs to the ValidatorFn type.

A TypeScript function containing dual return statements

Answer №1

Answer №2

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