为什么我的错误处理程序不能处理异步中间件抛出的异常？

Question

如果我有一个中间件，我通常会抛出这样的错误：

function throwMiddleware(req, res, next) {
  throw new Error(`Something went wrong in your async middleware.`);
}

这将被我的集中式错误处理中间件捕获。

但是，当我有一个异步中间件时，我会得到一个 UnhandledPromiseRejectionWarning：

async function throwMiddleware(req, res, next) {
  await new Promise((resolve) => {
    setTimeout(() => {
      resolve();
    }, 200);
  });
  throw new Error(`Something went wrong in your async middleware.`);
}

完整代码：

const express = require("express");

const app = express();
async function throwMiddleware(req, res, next) {
  await new Promise((resolve) => {
    setTimeout(() => {
      resolve();
    }, 200);
  });
  throw new Error(`Something went wrong in your async middleware.`);
}

app.get("/", throwMiddleware, (req, res, next) => { // route for GET /
  console.log("get /");
});

app.use((err, req, res, next) => { // centralized error handler
  if (res.headersSent) {
    return next(err);
  }

  console.log("error caught in middleware:", err.message);
  return res.send("oops");
});

app.listen(3500);

Answer 1

throwing 的错误我把它放在next 调用中。但我不知道为什么 throwing 在同步中间件中有效，而在异步中间件中无效。

async function throwMiddleware(req, res, next) {
  await new Promise((resolve) => {
    setTimeout(() => {
      resolve();
    }, 200);
  });
  next(new Error(`Something went wrong in your async middleware.`));
}

Answer 2

您可以在 express 中编写自己的错误处理程序，see the documentation here.

app.use(function (err, req, res, next) {
  console.error(err)
  res.status(500).send('this is handled error')
})

最后使用你的声明app.use。