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In Express.js, routing middleware can handle errors in the following ways:

• Error Handling Middleware: Express.js allows you to define error handling middleware, which will only be called when calling next(err). You can add multiple error handling middleware to the app, which will be called in the order it was added.

• try/catch block: In asynchronous middleware, you can use the try/catch block to catch errors thrown in asynchronous operations and pass the error to the error handling middleware by calling next(err).

• Pasting errors with next(): In any middleware, if an error occurs, you can call next(err) to pass the error object to the next middleware. If there are no more middleware in the current middleware chain, Express.js will look for an error handling middleware to handle this error.

• Custom Error Object: You can create custom error objects and pass them to next(), so that these errors can be recognized and processed accordingly in the error handling middleware.

• Use async/await: Using async/await in Express.js’ middleware can make the asynchronous code look like synchronous code and it can be easier to use the try/catch block to catch errors.

• Error object properties: In the error object, you can set properties such as status or statusCode, so that the error handling middleware can determine the HTTP status code of the response based on these properties.

• Log Recording: In error handling middleware, logging logic is usually also included to log details of errors, which is very important for debugging and monitoring applications.

• Client Error Response: In the error handling middleware, you can send an appropriate HTTP response to the client, including error messages and status codes, to notify the client that an error occurred.

In summary, routing middleware error handling in Express.js is mainly achieved by defining error handling middleware, using try/catch block, passing error objects to next(), and setting appropriate properties in the error object.

Error handling is an important part of ensuring the stability and user experience of Express.js applications. Through the above methods, developers can effectively capture and handle errors in the application while providing clear feedback to the client.