Angular strongly typed reactive forms

Question

I'm looking to refactor a large set of components in my Angular project to have strongly typed FormGroups, FormArrays, and FormControls.

I'm just looking for a good way to implement strongly typed reactive forms. Could anyone provide suggestions/recommendations from their own experiences?

Thank you.

EDIT:

To clarify, by strongly typed I mean currently when I create a FormGroup or FormArray I have no way to specify the structure of the actual form inside it. When I pass this form around to various components in my app, I then feel I am making it more difficult to maintain.

Answer 1

The most elegant solution is leveraging TypeScript declaration files (*.d.ts) to introduce generic interfaces extending the standard form classes like AbstractControl, FormControl, etc. It doesn’t introduce any new functionality and has no footprint in the compiled JavaScript, but at the same time enforcing strong type checking.

It was suggested by Daniele Morosinotto in March this year and there are talks now to include it in Angular 9.

Adopting the solution is straightforward:

1. Download TypedForms.d.ts from this gist and save it as src/typings.d.ts in your project (Angular 6+ already knows how to use this file).
2. Start using the new types (FormGroupTyped<T>, FormControlTyped<T>, etc.) whenever you need a strong type validation (see examples in that gist or stackblitz).

For more information, check out a blog post analysing available solutions for strongly typed forms.

Answer 2

I had a similar issue and this was my solution. I really only cared about the type of the 'value' of the form not the form itself. It ended up looking something like this.

export interface UserFormValue {
  first_name: string
  last_name: string
  referral: string
  email: string
  password: string
}
...

ngOnInit() {
  this.userForm = this.fb.group({
    first_name: [ '', Validators.required ],
    last_name: [ '', Validators.required ],
    referral: [ '' ],
    email: [ '', [ Validators.required, Validators.email ] ],
    password: [ '', [ Validators.required, Validators.minLength(8) ] ],
  });
}

...

Then in the template submit the value

<form [formGroup]="userForm" (ngSubmit)="onSubmit(userForm.value)">
   ...
</form>

Now you can add a type to the submit function

onSubmit(userForm: UserFormValue) {
   ...
}

It's not perfect but has been good enough for my use cases. I really wish there was like this.

userForm: FormGroup<UserFormValue>

Answer 3

For ones who want another solution. I found this article talking about strong type for angular form. Below is my sumary.

interface Person {
  name: string;
  email: string
}

// Controls in a form group that would emit a Person as it's value
type PersonControls = { [key in keyof Person]: AbstractControl };
type PersonFormGroup = FormGroup & { value: Person, controls: PersonControls };

export class MyFormComponent {
  form = new FormGroup({
    name: new FormControl(),
    email: mew FormControl()
  } as PersonControls) as PersonFormGroup;

  init() {
    const name = this.form.controls.name; // strong typed!
  }
}

Answer 4

The solution I ended up using was a library I found called ngx-strongly-typed-forms

It enables you to have strongly typed FormControls, FormGroups, and FormArrays. There are some limitations but it's definitely helped a lot in my project.

You can see the documentation at https://github.com/no0x9d/ngx-strongly-typed-forms