NestJs调用jwtService.decode报错：Cannot read properties of undefined

报错信息 #

[Nest] 16960 - 2022年12月19日 晚上10:22:28 ERROR [ExceptionsHandler]
Cannot read properties of undefined (reading 'decode') TypeError:
Cannot read properties of undefined (reading 'decode')

在 AdminGuard.canActivate (D:\Noum\Data\CYBRNODE\MAN STACK\Cybrnode-Blog-Backend\Cybr-Blog-Nest-Backend\src\guard\admin.guard.ts:28:34)

在 GuardsConsumer.tryActivate (D:\Noum\Data\CYBRNODE\MAN STACK\Cybrnode-Blog-Backend\Cybr-Blog-Nest-Backend\node_modules@nestjs\core\guards\guards-consumer.js:15:34)
在 processTicksAndRejections (node:internal/process/task_queues:96:5)

相关代码 #

类型定义 #

export type PayloadType = {
  id: string;
};

业务代码 #

let jwtService: JwtService;

let token = AuthenticationService.jwtToken.accessToken;
console.log(token);

if (token) {
  const payload = jwtService.decode(token.split('')[1]) as PayloadType;
  console.log(payload);
}

解决方案 #

• 修复JwtService未实例化问题
  你仅声明了jwtService的类型但未创建有效实例，Nest框架中必须通过构造函数依赖注入获取JwtService实例，修改AdminGuard代码如下：

  import { Injectable, ExecutionContext } from '@nestjs/common';
  import { JwtService } from '@nestjs/jwt';
  
  @Injectable()
  export class AdminGuard {
    // 通过构造函数注入JwtService实例
    constructor(private readonly jwtService: JwtService) {}
  
    async canActivate(context: ExecutionContext): Promise<boolean> {
      let token = AuthenticationService.jwtToken.accessToken;
      console.log(token);
  
      if (token) {
        // 使用注入的实例调用decode方法
        const payload = this.jwtService.decode(token.split(' ')[1]) as PayloadType;
        console.log(payload);
      }
      // 补充其他守卫逻辑...
      return true;
    }
  }
  

• 修复Token分割错误
  原代码中token.split('')[1]是按单个字符分割，会错误取到token的第二个字符。标准Bearer Token格式为Bearer xxxxxxxxxx，需按空格分割取第二部分，改为token.split(' ')[1]。

内容的提问来源于stack exchange，提问作者M Nouman