initial readme

Author: Chanlito

README.md

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+# NestJS Extensions
+
+[WIP] A bunch of useful and opinionated filters, modules, pipes... to use with Nest framework. 😻
+
+## Setup
+
+```bash
+npm install nestjs-extensions@latest
+```
+
+## Usage
+
+* `ApplicationExceptionFilter` is a nestjs filter use to catch all exceptions & errors in the application.
+
+  ```ts
+  import { ApplicationExceptionFilter } from 'nestjs-extensions';
+  // ... other imports
+
+  const app = await NestFactory.create();
+
+  app.useGlobalFilters(new ApplicationExceptionFilter());
+  ```
+
+* `DtoPipe` & `Dto` is used for validation. Internally it uses `class-transformer` & `class-validator`.
+
+  * *Step 1* - use the pipe, it requires a nestjs `Reflector`.
+
+  ```ts
+  import { DtoPipe } from 'nestjs-extensions';
+  // ... other imports
+
+  const app = await NestFactory.create();
+
+  app.useGlobalPipes(new DtoPipe(new Reflector()));
+  ```
+
+  * *Step 2* - create a file called `create-post.dto.ts`
+
+  ```ts
+  import { Transform } from 'class-transformer';
+  import { IsNotEmpty, IsOptional, IsString } from 'class-validator';
+  import { Dto } from 'nestjs-extensions';
+
+  @Dto()
+  export class CreatePostDto {
+    @IsNotEmpty()
+    @IsString()
+    title!: string;
+
+    @IsString()
+    @IsOptional()
+    description?: string;
+
+    @IsNotEmpty()
+    @Transform(x => +x)
+    count!: number;
+  }
+  ```
+
+  * *Step 3* - use it inside your controller
+
+  ```ts
+  // ...
+  @Controller('posts')
+  export class PostsController {
+    @Post()
+    async createPost(@Body() { title, description, count }: CreatePostDto) {
+      return { title, description, count };
+    }
+  }
+  ```