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javascript - 在 Express 中使用自定义错误中间件时未定义 next

问题描述

我正在尝试在 express 中使用 next() 将错误传递给以下路由中的自定义中间件：

app.post("/api/persons", (req, res) => {
  const findPerson = Person.findOne({ name: req.body.name });
  if (findPerson.length) {
    res.status(404).json({ error: "Name already exists" });
  } else if (req.body && req.body.name && req.body.number) {
    const person = new Person({
      name: req.body.name,
      number: req.body.number,
    });
    person
      .save()
      .then((savedPerson) => {
        console.log("saved successfully.");
        res.json(savedPerson).end();
      })
      .catch((err) => next(err));
    app.use(morgan("tiny"));
  } else {
    res.status(404).json({ error: "Name or number missing" });
  }
});

我已经定义了中间件功能如下：

const errorHandler = (error, request, response, next) => {
  console.error(error.message);

  if (error.name === "CastError") {
    return response.status(400).send({ error: "malformatted id" });
  }

  next(error);
};
app.use(errorHandler);

在所有其他 app.use() 之后，我将此中间件添加到文件的最后。但我不断收到如下参考错误：

UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch().

即使我清楚地使用了 catch 块，它似乎也会抛出错误。我尝试将错误处理程序的定义添加到顶部，但它仍然显示相同的错误。

标签： javascriptnode.jsexpress

解决方案

Change

app.post("/api/persons", (req, res) => { // next is missing here
 // ..///
});

To

app.post("/api/persons", (req, res, next) => { // add next  here
 // ../// next(err); // call next with error now
});

Since promises automatically catch both synchronous errors and rejected promises, you can simply provide next as the final catch handler and Express will catch errors, because the catch handler is given the error as the first argument.

Read - https://expressjs.com/en/guide/error-handling.html

For errors returned from asynchronous functions invoked by route handlers and middleware, you must pass them to the next() function, where Express will catch and process them.

function errorHandler (err, req, res, next) {
  if (res.headersSent) {
    return next(err)
  }
  res.status(500)
  res.render('error', { error: err })
}

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