Middleware Basics

Middleware runs before and after controller execution.

Request pipeline

Request
  -> Middleware A
  -> Middleware B
  -> Controller
  <- Middleware B
  <- Middleware A
Response

Typical middleware use cases

Authentication
Logging
Performance timing
Security checks
Data transformation
Rate limiting

Create a logger middleware

import { Middleware } from '@midwayjs/core';
import { Context, NextFunction } from '@midwayjs/koa';

@Middleware()
export class LoggerMiddleware {
  resolve() {
    return async (ctx: Context, next: NextFunction) => {
      const startTime = Date.now();
      console.log(`-> ${ctx.method} ${ctx.url}`);

      await next();

      const duration = Date.now() - startTime;
      console.log(`<- ${ctx.method} ${ctx.url} ${ctx.status} ${duration}ms`);
    };
  }
}

Register middleware

import { Configuration, App } from '@midwayjs/core';
import * as koa from '@midwayjs/koa';
import { LoggerMiddleware } from './middleware/logger.middleware';

@Configuration({
  imports: [koa],
})
export class MainConfiguration {
  @App()
  app: koa.Application;

  async onReady() {
    this.app.useMiddleware([LoggerMiddleware]);
  }
}

Verify in output panel

Visit GET /middleware-demo (or any route) and check logs in output.

Summary

Middleware wraps request lifecycle
await next() is required for proper flow
Register global middleware in onReady

Error Handling

Application Configuration

Files

Preparing Environment

npm install
npm run dev