Reactive forms validation for pros

I very much missed the ng-messages directive from AngularJS, so I created a similar set of directives to use in Angular 2+. In contrast to the directives from AngularJS, the directives in this library require passing the control name to the directive, instead of the control's errors. This allowed me to hook into the status of control, such as its dirty state, and display validation messages according to that status. The design of this library promotes less boilerplate code, which keeps your templates clean.

Features

• ✅ Simple syntax that reduces boilerplate
• ✅ Configure when to display error messages for an app further reducing boilerplate
• ✅ Seamless integration with Reactive Forms
• ✅ Works with nested forms

Table of Contents

• How it works
• Installation
• Usage
• Configuration
• Handling form submission
• Getting error details
• Styling
• Miscellaneous
• Development

How it works

There are a few rules that the library follows to determine when to display errors:

• Errors will be shown no matter what configuration you're using after form is submitted.
• If no configuration is provided, the errors will be shown when control is touched.
  • This is chosen due to the UX guidelines. Read (1) How to Report Errors in Forms and (2) Designing More Efficient Forms for more info.
• If you configured errors to be shown when formIsSubmitted, but dealing with a control that does not have a parent form, the config for this control will fall back to touched.

For more info about this see Advanced configuration.

Compatibility

| Angular | @ngspot/ngx-errors | |---------|--------------------| | >17.1 | 4.x | | >13.0 | 3.x | | >9.1 | 2.x |

Installation

NPM

npm install @ngspot/ngx-errors

Yarn

yarn add @ngspot/ngx-errors

Usage

Import library into application module:

@NgModule({
  imports: [
    NgxErrorsModule, // <-- include imported module in app module
  ],
})
export class MyAppModule {}

Use case with a form:

import { NGX_ERRORS_DECLARATIONS } from '@ngspot/ngx-errors'; // <-- import declarations

@Component({
  selector: 'my-component',
  standalone: true,
  imports: [ReactiveFormsModule, NGX_ERRORS_DECLARATIONS], // <-- include imported declarations in the imports
  template: `
    <form [formGroup]="myForm">
      <input formControlName="email" type="email" />

      <div ngxErrors="email">
        <div *ngxError="'required'">Email is required</div>
      </div>
    </form>
  `,
})
export class MyComponent implements OnInit {
  myForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.myForm = this.fb.group({
      email: ['', Validators.required],
    });
  }
}

Use case with a simple FormControl:

@Component({
  selector: 'my-component',
  standalone: true,
  imports: [ReactiveFormsModule, NGX_ERRORS_DECLARATIONS],
  template: `
    <input [formControl]="email" placeholder="Email" type="email" />

    <div [ngxErrors]="email">
      <div *ngxError="'required'">Email is required</div>
    </div>
  `,
})
export class MyComponent implements OnInit {
  email = new FormControl('', Validators.required);
}

Use case with a template driven form control:

@Component({
  selector: 'my-component',
  standalone: true,
  imports: [FormsModule, NGX_ERRORS_DECLARATIONS],
  template: `
    <input [(ngModel)]="email" #emailModel="ngModel" required type="email" />

    <div [ngxErrors]="emailModel.control">
      <div *ngxError="'required'">Email is required</div>
    </div>
  `,
})
export class MyComponent implements OnInit {
  email: string;
}

Configuration

Configure how and when the errors should show up by using provideNgxErrorsConfig() function either at the application level or at the component level:

At the application level:

import { provideNgxErrorsConfig } from '@ngspot/ngx-errors';

bootstrapApplication(AppComponent, {
  providers: [
    provideNgxErrorsConfig({
      showErrorsWhenInput: 'dirty',
      showMaxErrors: 1,
    })
  ]
}).catch((err) =>
  console.error(err)
);

At the component level

import { provideNgxErrorsConfig } from '@ngspot/ngx-errors';

@Component({
  ...
  providers: [
    provideNgxErrorsConfig({
      showErrorsWhenInput: 'dirty',
      showMaxErrors: 1,
    })
  ]
})
export class MyComponent { }

Here's the configuration object interface:

export interface IErrorsConfiguration {
  /**
   * Configures when to display an error for an invalid control. Options that
   * are available by default are listed below. Note, custom options can be
   * provided using CUSTOM_ERROR_STATE_MATCHERS injection token.
   *
   * `'touched'` - *[default]* shows an error when control is marked as touched. For example, user focused on the input and clicked away or tabbed through the input.
   *
   * `'dirty'` - shows an error when control is marked as dirty. For example, when user has typed something in.
   *
   * `'touchedAndDirty'` - shows an error when control is marked as both - touched and dirty.
   *
   * `'formIsSubmitted'` - shows an error when parent form was submitted.
   */
  showErrorsWhenInput?: string;

  /**
   * The maximum amount of errors to display per ngxErrors block.
   */
  showMaxErrors?: number;
}

Providing custom logic for displaying errors

By default, the following error state matchers for displaying errors can be used: 'touched', 'dirty', 'touchedAndDirty', 'formIsSubmitted'.

Custom error state matchers can be added using the CUSTOM_ERROR_STATE_MATCHERS injection token.

First, define the new error state matcher:

@Injectable({ providedIn: 'root' })
export class MyAwesomeErrorStateMatcher implements IErrorStateMatcher {
  isErrorState(
    control: AbstractControl | null,
    form: FormGroupDirective | NgForm | null
  ): boolean {
    return !!(control && control.value && /* my awesome logic is here */);
  }
}

Second, use the new error state matcher when providing CUSTOM_ERROR_STATE_MATCHERS in the AppModule:

providers: [
  {
    provide: CUSTOM_ERROR_STATE_MATCHERS,
    deps: [MyAwesomeErrorStateMatcher],
    useFactory: (myAwesomeErrorStateMatcher: MyAwesomeErrorStateMatcher) => {
      return {
        myAwesome: myAwesomeErrorStateMatcher,
      };
    },
  },
];

Now the string 'myAwesome' can be used either in the showErrorsWhenInput property of the configuration object or in the [showWhen] inputs.

Overriding global config

You can override the configuration specified through provideNgxErrorsConfig() function by using [showWhen] input on [ngxErrors] and on [ngxError] directives:

<div ngxErrors="control" showWhen="touchedAndDirty">
  <div *ngxError="'required'; showWhen: 'dirty'">
    This will be shown when control is dirty
  </div>

  <div *ngxError="'min'">
    This will be shown when control is touched and dirty
  </div>
</div>

Handling form submission

Often there's a requirement to submit a form when user presses Enter. Under the hood ngxError relies on form submit event to display errors. That is why it's important to trigger form submission properly rather than binding (keyup.enter) event to the method in your component class directly. Here's how to do that:

<form
  [formGroup]="form"
  (ngSubmit)="yourMethod()"
  (keyup.enter)="submitBtn.click()"
>
  ...

  <button #submitBtn>Submit</button>
</form>

Getting error details

Each control error in Angular may contain additional details. For example, here's what min error looks like:

const control = new FormControl(3, Validators.min(10));
const error = control.getError('min');
console.log(error); // prints: { min: 10, actual: 3 }

You can easily get access to these details in the template:

<div ngxErrors="control">
  <div *ngxError="'min'; let err">
    Number should be greater than {{ err.min }}. You've typed {{ err.actual }}.
  </div>
</div>

In the example above we're accessing error context through a variable err (can be anything you want).

Styling

ngxErrors directive can be applied to an element such as div or to an ng-container. If it's a div, that div can be targeted with the following CSS included in the global CSS file:

[ngxerrors] {
  color: red;
}

Integration with @angular/material

Angular Material inputs have their own way of setting logic for determining if the input needs to be highlighted red or not. If custom behavior is needed, a developer needs to provide appropriate configuration. @ngspot/ngx-errors configures this functionality for the developer under the hood. In order for this configuration to integrate with @angular/material inputs smoothly, use package @ngspot/ngx-errors-material. It also provides an additional optimization where mat-form-field component serves the purpose of ngxErrors directive.

Install:

npm install @ngspot/ngx-errors-material

Use:

import { NGX_ERRORS_MATERIAL_DECLARATIONS } from '@ngspot/ngx-errors-material'; // <-- import the declarations

@Component({
  selector: 'my-component',
  standalone: true,
  imports: [
    ReactiveFormsModule,
    MatInputModule,
    NGX_ERRORS_MATERIAL_DECLARATIONS, // <-- include imported declarations
  ],
  template: `
    <form [formGroup]="form">
      <mat-form-field>
        <mat-label>Name</mat-label>

        <input matInput formControlName="name" />

        <!-- 
          Note: there's no parent ngxErrors directive.
          mat-form-field serves the purpose ngxErrors directive.
        -->
        <mat-error *ngxError="'required'">Name is required</mat-error>
      </mat-form-field>
    </form>
  `
})
export class MyComponent {
  private fb = inject(FormBuilder);

  form = this.fb.group({
    name: this.fb.control('', { validators: [Validators.required] }),
  });
}

Miscellaneous

ngx-errors library provides a couple of misc function that ease your work with forms.

dependentValidator

Makes it easy to trigger validation on the control, that depends on a value of a different control

Example with using FormBuilder:

import { dependentValidator } from '@ngspot/ngx-errors';

export class LazyComponent {
  constructor(fb: FormBuilder) {
    this.form = fb.group({
      password: ['', Validators.required],
      confirmPassword: [
        '',
        dependentValidator<string>({
          watchControl: (f) => f!.get('password')!,
          validator: (passwordValue) => isEqualToValidator(passwordValue),
        }),
      ],
    });
  }
}

function isEqualToValidator<T>(compareVal: T): ValidatorFn {
  return function (control: AbstractControl): ValidationErrors | null {
    return control.value === compareVal
      ? null
      : { match: { expected: compareVal, actual: control.value } };
  };
}

The dependentValidator may also take condition. If provided, it needs to return true for the validator to be used.

const controlA = new FormControl('');
const controlB = new FormControl(
  '',
  dependentValidator<string>({
    watchControl: () => controlA,
    validator: () => Validators.required,
    condition: (val) => val === 'fire',
  })
);

In the example above, the controlB will only be required when controlA value is 'fire'

extractTouchedChanges

As of today, the FormControl does not provide a way to subscribe to the changes of touched status. This function lets you do just that:

* const touchedChanged$ = extractTouchedChanges(formControl);

markDescendantsAsDirty

As of today, the FormControl does not provide a way to mark the control and all its children as dirty. This function lets you do just that:

markDescendantsAsDirty(formControl);

Development

Basic Workflow

One time config: git config --global push.followTags true

1. Develop
2. Write specs
3. Run npm run test:lib
4. Run npm run commit and choose fix or feature
5. Run npm run release
6. Run npm run build:lib
7. Go to the dist directory and run npm publish
8. Push changes git push

Scripts

• build:lib - Builds the library
• test:lib - Runs tests
• test:lib:headless - Runs tests in headless mode with Chrome
• release - Releases a new version; this will bump the library's version and update the CHANGE_LOG file based on the commit message
• release:first - Creates the first release
• commit - Creates a new commit message based on Angular commit message convention
• contributors:add - Adds a new contributor to the README file

License

MIT © Dmitry Efimenko

Contributors ✨

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!