Custom parameter decorators

Parameter decorators are there to simplify the task of geting a specific data you need by using the request (req) object or by generating it. For example the @Body decorator we provide simply returns the req.body object.

By using the createParamDecorator function, you can create your own decorators that fulfill the needs of your application.

As a basic example, let's get the browser information of the client via a decorator.

First we create our decorator:

import { createParamDecorator } from 'next-api-decorators';

export const UserAgent = createParamDecorator<string | undefined>(
  req => req.headers['user-agent']
);

Later we can use the decorator in our handler:

...
class CommentHandler {
  @Get()
  public comments(@UserAgent() userAgent?: string) {
    return `Someone requested the comments via "${userAgent ?? 'Unknown browser'}"`;
  }
}
...