Custom Middleware

Preview — 3 of 10 questions

You want a lightweight middleware with no dependencies to inject. Which form is most appropriate?

javascript

import { Request, Response, NextFunction } from 'express';

export function correlationId(req: Request, _res: Response, next: NextFunction): void {
  req.headers['x-correlation-id'] ??= crypto.randomUUID();
  next();
}

// in module
consumer.apply(correlationId).forRoutes('*');

AA plain function (req, res, next) => { ... } passed to consumer.apply()

BAn interceptor returned from @Module()

CA guard implementing canActivate

DA class implementing NestMiddleware registered in providers

What does consumer.apply(MiddlewareA, MiddlewareB).forRoutes('cats') do?

javascript

consumer
  .apply(MiddlewareA, MiddlewareB)
  .forRoutes('cats'); // order: A -> B -> handler

AOnly MiddlewareA runs; MiddlewareB is ignored

BBoth run on cats routes in the order they are listed: A then B

CThey run in reverse order: B then A

DThey run in parallel with no ordering guarantee

How do you apply a middleware to all controller routes except cats/health?

javascript

import { RequestMethod } from '@nestjs/common';

consumer
  .apply(LoggerMiddleware)
  .exclude({ path: 'cats/health', method: RequestMethod.GET })
  .forRoutes(CatsController);

Aconsumer.apply(M).forRoutes('cats').not('cats/health')

Bconsumer.apply(M).forRoutes('cats/*').skip('cats/health')

CExclusion is impossible; you must list every included route

Dconsumer.apply(M).exclude('cats/health').forRoutes(CatsController)

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