[ngx-formly] Use Angular Formly Extensions to automatically localize all field labels

In this lesson we're diving a bit deeper and learn how to inject services into Formly Extensions with the example of using ngx-translate to localize all of our form field labels.

Create Extension with Tranlsate service:

// translate.extension.ts
import { TranslateService } from '@ngx-translate/core';
import { FormlyFieldConfig } from '@ngx-formly/core';

export class TranslateExtension {
  constructor(private translate: TranslateService) {}

  prePopulate(field: FormlyFieldConfig) {
    const to = field.templateOptions || {};

    if (!to.label || to._translated) {
      return;
    }

    to._translated = true;
    field.expressionProperties = {
      ...(field.expressionProperties || {}),
      'templateOptions.label': this.translate.stream(
        field.templateOptions.label
      )
    };
  }
}

export function registerTranslateExtension(translate: TranslateService) {
  return {
    extensions: [
      {
        name: 'translate-extension',
        extension: new TranslateExtension(translate)
      }
    ]
  };
}

Define in module:

import { registerTranslateExtension } from './translate.extension';

// AoT requires an exported function for factories
export function HttpLoaderFactory(httpClient: HttpClient) {
  return new TranslateHttpLoader(httpClient, 'assets/i18n/', '.json');
}

export function minValidationMessage(err, field: FormlyFieldConfig) {
  return `Please provide a value bigger than ${err.min}. You provided ${err.actual}`;
}

export function ipValidationMessage(err, field: FormlyFieldConfig) {
  return `"${field.formControl.value}" is not a valid IP address`;
}

export function IpValidator(control: FormControl): ValidationErrors {
  return !control.value || /(d{1,3}.){3}d{1,3}/.test(control.value)
    ? null
    : { ip: true };
}

@NgModule({
  declarations: [AppComponent, NgSelectFormlyComponent],
  imports: [
    BrowserModule,
    SharedModule,
    AppRoutingModule,
    BrowserAnimationsModule,
    ReactiveFormsModule,
    NgSelectModule,
    HttpClientModule,
    TranslateModule.forRoot({
      loader: {
        provide: TranslateLoader,
        useFactory: HttpLoaderFactory,
        deps: [HttpClient]
      }
    }),
    FormlyModule.forRoot({
      validators: [
        {
          name: 'ip',
          validation: IpValidator
        }
      ],
      validationMessages: [
        {
          name: 'required',
          message: 'This field is required'
        },
        {
          name: 'min',
          message: minValidationMessage
        },
        {
          name: 'ip',
          message: ipValidationMessage
        }
      ],
      types: [
        {
          name: 'my-autocomplete',
          component: NgSelectFormlyComponent
        }
      ],
      extensions: [
        {
          name: 'data-cy- extension',
          extension: dataCyExtension
        }
      ]
    }),
    FormlyMaterialModule
  ],
  providers: [
    {
      provide: FORMLY_CONFIG,
      multi: true,
      useFactory: registerTranslateExtension,
      deps: [TranslateService]
    }
  ],
  bootstrap: [AppComponent]
})
export class AppModule {}