> For the complete documentation index, see [llms.txt](https://mandarineframework.gitbook.io/mandarine-ts/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/custom-middleware.md).

# Custom Middleware

{% hint style="info" %}
For this article, it is necessary to have a understanding of [Middleware component](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-core/components/middleware), [Controllers](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/controllers), [Routes](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/controllers/using-routes-and-http-handlers) & [HTTP Handlers](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/controllers/http-handlers)
{% endhint %}

## Main

Custom middleware are used to provide interceptions to certain endpoints in your Application. The use cases may vary, but the most common use cases are verifications.

In order for a middleware to be considered a *mandarine middleware,* your middleware class needs to **implement** the class [MiddlewareTarget](https://doc.deno.land/https/raw.githubusercontent.com/mandarineorg/mandarinets/master/main-core/components/middleware-component/middlewareTarget.ts).

[MiddlewareTarget](https://doc.deno.land/https/raw.githubusercontent.com/mandarineorg/mandarinets/master/main-core/components/middleware-component/middlewareTarget.ts) contains two key methods which you will need to provide functionality.

* `onPreRequest(...args): boolean`
  * It is executed before the request reaches to the [HTTP Handler](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/controllers/http-handlers). 
  * If it returns **true,** the request is authorized to continue to the *HTTP handler* & then to *the post-request handler*.
  * If it returns **false**, the request will be stopped and the *HTTP handler* nor the *post-request handler* will  be reached.
* `onPostRequest(...args): void`
  * It is executed after the request has reached & called the *HTTP handler.*

**Note** that both `onPreRequest` and `onPostRequest` **can** absolutely use all [HTTP parameter decorators](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-mvc/controllers/http-handlers#http-parameter-decorators).

## Usage

**Syntax:** [See syntax and extra information here](https://mandarineframework.gitbook.io/mandarine-ts/mandarine-core/components/middleware#usage)

```typescript
middleware.ts

import { Middleware, MiddlewareTarget } from "https://deno.land/x/mandarinets/mod.ts";

@Middleware(new RegExp('/api/*'))
export class Middleware1 implements MiddlewareTarget {

    public onPreRequest(@ResponseParam() response: any): boolean {
        console.log("pre-request()");
        return true;
    }
    
    public onPostRequest(): void {
        console.log("post-request()");
    }
}
```

```typescript
controller.ts

import { Controller, MandarineMVC } from "https://deno.land/x/mandarinets/mod.ts";

@Controller()
export class MyController {

    @GET('/api/hello-world')
    public helloWorldApi() {
        return "Hello world";
    }

}
```

{% tabs %}
{% tab title="Index file" %}

```typescript
import { MandarineCore } from "https://deno.land/x/mandarinets/mod.ts";

import { MyController } from "./controller.ts";
import { Middleware1 } from "./middleware.ts";

const controllers = [MyController1];
const middleware = [Middleware1];

new MandarineCore().MVC().run();
```

{% endtab %}

{% tab title="Deno execution" %}

```bash
deno run --config tsconfig.json --allow-net --allow-read index.ts
```

{% endtab %}
{% endtabs %}

Result

```bash
# http://localhost:8080/api/hello-world
[Console] pre-request()
Hello world
[Console] post-request()
```


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