TL;DR
We are building the documentation of@myndpm/dyn-forms atmynd.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, akaValidators andAsyncValidators, 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 defaultValidators that we're used to consume programatically in our Reactive Forms, some of them are Validator Functions (ValidatorFn) likeValidators.required, and some others are Validator Factories ((args) => ValidatorFn) which builds a Validator based on a required parameter likeValidators.minLength(4).

The definition of a Validator Function is:

(control:AbstractControl)=>ValidationErrors|null

it receives the control to be validated, and returnsnull 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:

functionminLength(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 anid and a factoryfn:

exportinterfaceDynControlValidator{id:string;fn:(...args:any[])=>ValidatorFn;}

Theid 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 andmax.

The notation to use them in the Config Object is as follows:

// without parametersvalidators:['required'],// with parameters as arrayvalidators:['required',['min',1]],// with parameters as objectvalidators:{required:null,minLength:4},// with an inline ValidatorFn or ValidatorFn factoryvalidators:[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 ourValidatorFn Factory with anid and afn. 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';constvalidators:DynControlValidator[]=[{id:'email',fn:():ValidatorFn=>{return(control:AbstractControl)=>{// implement my validator// to return { email: true } | null;}}}];@NgModule({imports:[DynFormsModule.forFeature({validators,priority:100});

note thepriority 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 yourfn with anid 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 objectasyncValidators:[['myAsyncValidatorId',args]],// your factory will receive fn(args)// multiple arguments in array to be destructuredasyncValidators:[['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 andAsyncValidators as we just saw,Matchers andConditions to manipulate the controls under some special requirements, and alsoParamFns 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?

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