Fastify decorate未注册中间件：TypeScript中authenticate装饰器报错

我将原生JS的JWT校验中间件转为TypeScript后，使用fastify.decorate注册的authenticate方法，在路由中调用时提示类型错误，找不到该属性。

相关代码 #

authMiddleware.ts #

import fp from "fastify-plugin";
import fastifyJwt from "@fastify/jwt";
import { FastifyInstance, FastifyRequest, FastifyReply } from "fastify";

const authenticatePlugin = fp<FastifyInstance>(async (fastify, opts) => {
  fastify.register(fastifyJwt, {
    secret: "secret",
  });

  fastify.decorate(
    "authenticate",
    async (request: FastifyRequest, reply: FastifyReply) => {
      try {
        await request.jwtVerify();
      } catch (err) {
        reply.send(err);
      }
    }
  );
});

export default authenticatePlugin;

Index.ts（API入口） #

const server = fastify({
  logger: pino({ level: "info" }),
});

server.register(authenticatePlugin);
server.register(db, { uri });
server.register(MatchRoute);
server.register(AuthRoutes);

const start = async () => {
  try {
    await server.listen({ port: 7000 });
    console.log("Server started successfully");
  } catch (err) {
    server.log.error(err);
    process.exit(1);
  }
};
start();

路由调用（报错位置） #

fastify.post<{ Body: MatchAttributes }>(
  "/matches",
  {
    onRequest: [fastify.authenticate],
  },
  async (request, reply) => {
    // 路由逻辑
  }
);

报错信息 #

Property 'authenticate' does not exist on type 'FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse, FastifyBaseLogger, FastifyTypeProviderDefault>'.ts(2339)

解决步骤 #

1. 添加Fastify类型扩展声明 #

在项目中创建fastify.d.ts类型声明文件，扩展FastifyInstance接口：

import { FastifyRequest, FastifyReply } from "fastify";

declare module "fastify" {
  interface FastifyInstance {
    authenticate: (request: FastifyRequest, reply: FastifyReply) => Promise<void>;
  }
}

2. 配置TypeScript识别声明文件 #

修改tsconfig.json的include字段，确保包含上述声明文件：

{
  "compilerOptions": {
    // 其他配置
  },
  "include": [
    "src/**/*.ts",
    "fastify.d.ts" // 加入此行
  ]
}

3. 优化插件泛型定义 #

去掉authMiddleware.ts中fastify-plugin的显式泛型参数，让类型自动推断：

// 原代码
const authenticatePlugin = fp<FastifyInstance>(async (fastify, opts) => {
// 修改后
const authenticatePlugin = fp(async (fastify, opts) => {

完成以上操作后，TypeScript就能正确识别fastify.authenticate装饰器，不会再抛出类型错误。

内容的提问来源于stack exchange，提问作者cw23