概览

在使用 Express 开发 Web 应用程序时，有效地处理错误和管理未匹配任何定义处理程序的路由至关重要。这确保了应用程序的健壮性和更好的用户体验。

Express 中的错误处理

Express 通过中间件提供了内置的错误处理机制。在 Express 应用程序中进行适当的错误处理包括定义错误处理中间件函数，以捕获错误并作出相应响应。

分步指南

1. 创建错误处理中间件

错误处理中间件定义了四个参数：err、req、res 和 next。

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('出错了！');
});

2. 使用 next()

next() 函数至关重要。它将错误传递给链中的下一个错误处理中间件。在路由处理程序或其他中间件中，调用 next(err) 将错误传递给错误处理程序。

app.get('/route', (req, res, next) => {
  try {
    // ... 您的逻辑
  } catch (err) {
    next(err);
  }
});

3. 处理异步错误

对于异步代码，使用 catch 或与 promises 和 async/await 一起使用 next 来处理错误。

app.get('/async-route', async (req, res, next) => {
  try {
    // 尝试运行异步操作
    const data = await someAsyncOperation();
    // 如果成功，将数据发送回客户端
    res.send(data);
  } catch (err) {
    // 如果 someAsyncOperation() 中发生错误，捕获它
    // 然后将错误传递给下一个错误处理中间件
    next(err);
  }
});

处理未匹配的路由

未处理的路由是指不匹配任何定义路由的请求。优雅地处理这些路由是一个良好的实践。

处理未处理路由的步骤

1. 定义全捕获路由

在所有路由之后，添加一个全捕获路由处理程序。

app.use('*', (req, res) => {
  res.status(404).send('404 - 未找到');
});

这将捕获对未定义路由的任何请求，并返回 404 状态码。

2. 自定义响应

您可以根据需要自定义 404 响应，比如渲染一个 404 页面或返回一个 JSON 响应。

app.use('*', (req, res) => {
  res.status(404).render('NotFound');
});

结论

在 Express 中适当地处理错误和管理未匹配的路由是稳定和用户友好 Web 应用程序的关键组成部分。通过实施这些策略，您可以确保您的应用程序行为可预测，并在发生错误或访问错误路由时为用户提供信息性反馈。

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English version: Handling Errors and Unhandled Routes in Express

Overview

When developing web applications with Express, it's crucial to handle errors effectively and manage routes that do not match any defined handlers. This ensures a robust application and a better user experience.

Error Handling in Express

Express provides a built-in mechanism for error handling through middleware. Proper error handling in an Express application involves defining error-handling middleware functions that catch errors and respond accordingly.

Step-by-Step Guide

1. Creating an Error Handling Middleware

An error handling middleware is defined with four arguments: err, req, res, and next.

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

2. Using next()

The next() function is crucial. It passes the error to the next error handling middleware in line. In your route handlers or other middleware, call next(err) to pass errors to your error handler.

app.get('/route', (req, res, next) => {
  try {
    // ... your logic
  } catch (err) {
    next(err);
  }
});

3. Handling Asynchronous Errors

For asynchronous code, use catch or next with promises and async/await to handle errors.

app.get('/async-route', async (req, res, next) => {
  try {
    // Attempt to run the asynchronous operation
    const data = await someAsyncOperation();
    // If successful, send the data back to the client
    res.send(data);
  } catch (err) {
    // If an error occurs in someAsyncOperation(), catch it
    // Then pass the error to the next error handling middleware
    next(err);
  }
});

Handling Unmatched Routes

Unhandled routes are requests that do not match any of the defined routes. It's good practice to handle these gracefully.

Steps for Handling Unhandled Routes

1. Define a Catch-All Route

After all your routes, add a catch-all route handler.

app.use('*', (req, res) => {
  res.status(404).send('404 - Not Found');
});

This will catch any requests to undefined routes and return a 404 status code.

2. Customize the Response

You can customize the 404 response as needed, maybe rendering a 404 page or returning a JSON response.

app.use('*', (req, res) => {
  res.status(404).render('NotFound');
});

Conclusion

Proper error handling and managing unmatched routes in Express are key components of a stable and user-friendly web application. By implementing these strategies, you can ensure that your application behaves predictably and provides informative feedback to the user in case of errors or incorrect route access.