TL;DR
We are building the documentation of@myndpm/dyn-forms
at mynd.dev and we've added support for a variety of custom functions like Validators, AsyncValidators, Matchers, Conditions and more.
The next crucial part of any form is validation, aka Validators
and AsyncValidators
, and we took some time to study a nice way to implement them and we picked the most declarative one:
createMatConfig('INPUT', {
name: 'quantity',
validators: ['required', ['min', 1] ],
asyncValidators: ['myAsyncValidator'],
Angular Validators
Angular provides default Validators that we're used to consume programatically in our Reactive Forms, some of them are Validator Functions (ValidatorFn
) like Validators.required
, and some others are Validator Factories ((args) => ValidatorFn
) which builds a Validator based on a required parameter like Validators.minLength(4)
.
The definition of a Validator Function is:
(control: AbstractControl) => ValidationErrors | null
it receives the control to be validated, and returns null
if its value is valid, or an error object of the form { [error: string]: any }
Validator Factories are high-order functions that builds a Validator Function according some input parameters:
function minLength(minLength: number): ValidatorFn {
return (control: AbstractControl) => {
return (control.value && control.value.length < minLength)
? { minLength: true } // invalid
: null; // valid
}
}
as you can see, this is a very nice way to parametrize our Functions, so we defined the provisioning of Validators (and all the other handlers) with an id
and a factory fn
:
export interface DynControlValidator {
id: string;
fn: (...args: any[]) => ValidatorFn;
}
The id
will be the string that we will use in our Configuration Object. By default, @myndpm/dyn-forms
provide the default Angular Validators with the same name as we know them: required
, requiredTrue
, email
, pattern
, minLength
, maxLength
, min
and max
.
The notation to use them in the Config Object is as follows:
// without parameters
validators: ['required'],
// with parameters as array
validators: ['required', ['min', 1] ],
// with parameters as object
validators: { required: null, minLength: 4 },
// with an inline ValidatorFn or ValidatorFn factory
validators: [myValidatorFn, myValidatorFactory(args)],
supporting these different notations is unexpensive and can be useful for different kind of systems or developer tastes.
Custom Validators
As mentioned, all we need is to provide our ValidatorFn
Factory with an id
and a fn
. So we can easily provide them in our module with a code like this:
import { AbstractControl, ValidatorFn } from '@angular/forms';
import { DynFormsModule } from '@myndpm/dyn-forms';
import { DynControlValidator } from '@myndpm/dyn-forms/core';
const validators: DynControlValidator[] = [
{
id: 'email',
fn: (): ValidatorFn => {
return (control: AbstractControl) => {
// implement my validator
// to return { email: true } | null;
}
}
}
];
@NgModule({
imports: [
DynFormsModule.forFeature({ validators, priority: 100 });
note the priority
parameter to override the default validators (which weight is 0); we will play with priorities in a further article.
AsyncValidators
Providing async validators works in the same way. You provide your fn
with an id
and use them in the Config Object:
createMatConfig('INPUT', {
name: 'quantity',
validators: ['required'],
asyncValidators: ['myAsyncValidatorId'],
and if you need to provide arguments to your AsyncValidator factory, you can use:
// single argument which can be an object
asyncValidators: [['myAsyncValidatorId', args]],
// your factory will receive fn(args)
// multiple arguments in array to be destructured
asyncValidators: [['myAsyncValidatorId', [arg1, arg2]]],
// your factory will receive fn(arg1, arg2)
Custom Handlers
With this notation we added support for multiple kinds of functions that we require in the Dynamic Forms: Validators
and AsyncValidators
as we just saw, Matchers
and Conditions
to manipulate the controls under some special requirements, and also ParamFns
to inject functions to the parameters of the DynControls too.
We will be digging into the conditional executions in the next chapter.
In the meantime, what do you think of this notation?
// PS. We are hiring!
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