TypeScript：开发环境中出现“逗号运算符左侧未使用且没有副作用”错误

Question

问题

当我尝试使用

npm run dev:server

启动我的开发环境时，我收到此错误：

return new TSError(diagnosticText, diagnosticCodes);
           ^
TSError: ⨯ Unable to compile TypeScript:
src/routes/snippets.ts:6:26 - error TS2695: Left side of comma operator is unused and has no side effects.

6 exports.snippetRouter = (0, express_1.Router)();

然后服务器崩溃。但是当我运行

npm run build

项目时，编译时没有任何错误。然后我可以运行

node build/server.js

，一切都会按预期进行。我的编辑器中也没有收到任何错误或警告。

我寻找类似的错误，但找不到任何与我的情况匹配的内容。

有什么想法我可以尝试解决这个问题吗？

还值得一提的是，如果我从

app.use('/api/snippets', snippetRouter)

注释/删除

server.ts

行并运行

npm run dev:server

一切都会正常工作（当然缺少的功能除外）。

项目

项目结构：

src
├── controllers
|   └── snippets.ts
├── middleware
│   ├── index.ts
|   └── asyncWrapper.ts
├── routes
|   └── snippets.ts
└── server.ts

控制器/snippets.ts

import { Request, Response, NextFunction } from 'express';
import { asyncWrapper } from '../middleware';

export const createSnippet = asyncWrapper(
  async (req: Request, res: Response, next: NextFunction): Promise<void> => {
    res.status(201).json({
      data: "test msg"
    });
  }
);

中间件/asyncWrapper.ts

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

type Foo = (req: Request, res: Response, next: NextFunction) => Promise<void>;

export const asyncWrapper =
  (foo: Foo) => (req: Request, res: Response, next: NextFunction) => {
    return Promise.resolve(foo(req, res, next)).catch(next);
  };

路线/snippets.ts

import { Router } from 'express';
import { createSnippet } from '../controllers/snippets';

export const snippetRouter = Router();

snippetRouter.route('/').post(createSnippet);

服务器.ts

import express from 'express';
import { snippetRouter } from './routes/snippets';

const app = express();
app.use('/api/snippets', snippetRouter);

app.listen(5000, () => {
  console.log('Server is working');
});

package.json

{
  "name": "snippet-hub",
  "version": "1.0.0",
  "description": "",
  "main": "src/server.ts",
  "scripts": {
    "init:client": "npm install --prefix=client",
    "init:server": "npm install",
    "init": "npm-run-all -n init:**",
    "dev:client": "npm start --prefix=client",
    "dev:server": "nodemon src/server.ts",
    "dev": "npm-run-all -n --parallel dev:**",
    "build:clear": "rm -rf build",
    "build:tsc": "tsc",
    "build": "npm-run-all -n build:**"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/express": "^4.17.13",
    "@types/node": "^16.9.2",
    "@types/validator": "^13.6.3",
    "nodemon": "^2.0.12",
    "npm-run-all": "^4.1.5",
    "ts-node": "^10.2.1",
    "typescript": "^4.4.3"
  },
  "dependencies": {
    "dotenv": "^10.0.0",
    "express": "^4.17.1",
    "sequelize": "^6.6.5",
    "sqlite3": "^5.0.2",
    "umzug": "^3.0.0-beta.16"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "es6",
    "module": "commonjs",
    "outDir": "./build",
    "rootDir": "./src",
    "strict": true,
    "noImplicitAny": false,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src"]
}

Answer 1

我有同样的错误，我修复它的方法是导入express而不是解构它，然后从express调用路由器。将文件

routes/snippets.ts

调整到下面解决了问题

import express from 'express';
export const snippetRouter = express.Router();

snippetRouter.route('/').post(createSnippet);

以上解决了问题

Answer 2

当我通过返回由 {} 包围的键值对对象来使用箭头函数时遇到问题。以下是问题发生时的代码

const methodTest=(value)=>{ key1 : value,key2:value } 

解决方案是在大括号 {} 周围添加一个 () 示例：下面是对我有用的解决方案

const methodTest=(value)=>({key1:value , key2:value })

Answer 3

就我而言，问题是我本来打算动态评估对象文字，但我无意中创建了一个块作用域，并且接下来的语法不再有效。我有一个与以下人为示例类似的片段：

{
    phone: () => console.log('phone'),
    email: () => console.log('email'),
}[magicField.type]();

解决方案是用括号将大括号括起来，以便将它们解释为对象文字（如果这是您的意图）：

({
    phone: () => console.log('phone'),
    email: () => console.log('email'),
})[magicField.type]();