Type safety

nestjs-i18n can generate types! This way your translations will be completely type safe! 🎉

To use generated types specify the typesOutputPath option to let nestjs-i18n know where to put them.

src/app.module.ts

import { Module } from '@nestjs/common';
import * as path from 'path';
import { I18nModule } from 'nestjs-i18n';

@Module({
  imports: [
    I18nModule.forRoot({
      fallbackLanguage: 'en',
      loaderOptions: {
        path: path.join(__dirname, '/i18n/'),
        watch: true,
      },
      typesOutputPath: path.join(__dirname, '../src/generated/i18n.generated.ts'),
    }),
  ],
  controllers: [],
})
export class AppModule {}

The typesOutputPath should also be added to eslintignore to prevent linting errors.

Usage

To use the types within your code import the I18nTranslations type from the generated file. Pass this type into the generic type properties of the I18nContext or I18nService.

src/app.controller.ts

import { Controller, Get } from '@nestjs/common';
import { I18n, I18nContext } from 'nestjs-i18n';
import { I18nTranslations } from './generated/i18n.generated.ts';

@Controller()
export class AppController {

  @Get()
  async getHello(@I18n() i18n: I18nContext<I18nTranslations>) {
    return await i18n.t('test.HELLO');
  }
}

tip

You can import the I18nPath type so you require a valid i18n path in your code. This is useful when handeling exceptions with translations.

src/app.controller.ts

import { I18nPath } from './generated/i18n.generated.ts';

export class ApiException extends Error {
  get translation(): I18nPath {
    return this.message as I18nPath;
  }

  get args(): any {
    return this._args;
  }

  constructor(key: I18nPath, private readonly _args?: any) {
    super(key);
  }
}

caution

For now type safety is optional and need to be enabled. We're planning to make a breaking change where type safety is enabled by default.

Type safety with DTOS

You can also use the generated types in your DTOs. This way you can reduce the chance of having a typo in your validation messages.

src/craete-user.dto.ts

import { I18nTranslations } from './generated/i18n.generated.ts';
import {
  IsEmail,
  IsNotEmpty,
} from 'class-validator';
import { i18nValidationMessage } from 'nestjs-i18n';

export class CreateUserDto {
  @IsNotEmpty({ message: i18nValidationMessage<I18nTranslations>("validation.isNotEmpty")})
  @IsEmail({}, { message: i18nValidationMessage<I18nTranslations>("validation.isEmail")})
  email: string;

  @IsNotEmpty({ message: i18nValidationMessage<I18nTranslations>("validation.isNotEmpty")})
  password: string;

}