Node.js错误处理设置未按预期工作

Question

I am trying to have all my error messages in one file, each error is denoted by an error code, then in my functions/services, when there is an error, I call a function that takes the error code as an argument, then returns an object to the client with the error code and the respective error message from the errors.js file. as an example, a user trying to register with an email that already exists in the database, here is how I try to do it:

 // userService.js -- where my register function is const { errorThrower } = require('../../utils/errorHandlers'); ... static async registerNewUser(body) { const exists = await User.where({ email: body.email }).fetch(); if(exists) { errorThrower('400_2'); } ... } 

errorHandlers.js file:

 exports.errorThrower = (errCode) => { throw Object.assign(new Error(errors[errorCode]), { errorCode }) } exports.errorHandler = (err, req, res, next) => { if(!err.status && err.errorCode) { err.status = parseInt(err.errorCode.toString().substring(0, 3), 10); } let status, message if (err.status) { status = err.status message = err.message } else { status = 500; message = 'unexpected behavior, Kindly contact our support team!' } res.status(status).json({ errorCode: err.errorCode, message }) } 

errors.js

 module.exports = { '400_1': 'JSON payload is not valid', '400_2': 'user already registered', ... } 

 ... const user = require('./routes/user'); const { errorHandler } = require('../utils/errors'); ... app.use('/user' , user); app.use(errorHandler); ... 

now with this setup, when hitting the register endpoint by postman, I only get the following in the console

UnhandledPromiseRejectionWarning: Error: user already registered

could someone please tell me what am I missing here? thanks in advance!

Answer 1

You're not catching the error which you throw inside your errorThrower , thus getting the error UnhandledPromiseRejectionWarning . What you need to do is catch the error and pass it on the the next middleware, in order for the errorHandler -middleware to be able to actually handle the error. Something like this:

exports.register = async(req, res) => {
   try {
       await registerNewUser(req.body);
   } catch(err) {
       next(err);
   }
};

If you don't want to do this for every middleware, you could create a "base"-middleware which handles this:

const middlewareExecutor = async (req, res, next, fn) => {
    try {
        return await fn.call(fn, req, res, next);
    } catch (err) {
        next(err);
    }
};

Now you can pass your middlewares as an argument and delegate handling the error to the executor:

app.use('/user' , async (req, res, next) => middlewareExecutor(req, res, next, user));