哪些错误将由 express error 处理，哪些由 uncaughtException 错误处理程序处理？

Question

在我的服务中使用 express nodejs。我知道 express error handler，err first

的回调函数

app.use(function(err, req, res, next)

我们也可以通过

处理uncaughtException

process.on('uncaughtException', function(err) {}

其实有些uncaughtException会去express error handler而不是uncaughtException handler。

请帮忙告诉我哪些错误将由 express 处理，哪些由 uncaughtException 处理程序处理？

非常感谢

Answer 1

当您在直接从 Express 调用的函数中抛出异常 (throw new Error(...)) 时，它将被捕获并将其转发给您的错误处理程序。发生这种情况是因为您的代码周围有一个 try-catch 块。

app.get("/throw", function(request, response, next) {
    throw new Error("Error thrown in scope of this function. Express.js will delegate it to error handler.")
});

当您在不是直接从 Express（延迟或异步代码）调用的函数中抛出异常时，没有可用的 catch 块来捕获此错误并正确处理它。例如，如果您有异步执行的代码：

app.get("/uncaught", function(request, response, next) {
    // Simulate async callback using setTimeout.
    // (Querying the database for example).
    setTimeout(function() {
        throw new Error("Error thrown without surrounding try/catch. Express.js cannot catch it.");
    }, 250);
});

此错误不会被 Express 捕获（并转发给错误处理程序），因为此代码周围没有包装 try/catch 块。在这种情况下，将改为触发未捕获的异常处理程序。

一般来说，如果您遇到无法恢复的错误，请使用 next(error) 将此错误正确转发给您的错误处理程序中间件：

app.get("/next", function(request, response, next) {
    // Simulate async callback using setTimeout.
    // (Querying the database for example).
    setTimeout(function() {
        next(new Error("Error always forwarded to the error handler."));
    }, 250);
});

下面是一个完整的例子：

var express = require('express');

var app = express();

app.get("/throw", function(request, response, next) {
    throw new Error("Error thrown in scope of this function. Express.js will delegate it to error handler.")
});

app.get("/uncaught", function(request, response, next) {
    // Simulate async callback using setTimeout.
    // (Querying the database for example).
    setTimeout(function() {
        throw new Error("Error thrown without surrounding try/catch. Express.js cannot catch it.");
    }, 250);
});

app.get("/next", function(request, response, next) {
    // Simulate async callback using setTimeout.
    // (Querying the database for example).
    setTimeout(function() {
        next(new Error("Error always forwarded to the error handler."));
    }, 250);
});


app.use(function(error, request, response, next) {
    console.log("Error handler: ", error);
});

process.on("uncaughtException", function(error) {
    console.log("Uncaught exception: ", error);
});

// Starting the web server
app.listen(3000);

哪些错误将由 express error 处理，哪些由 uncaughtException 错误处理程序处理？

Which error will be handled by express error and which by uncaughtException error handler?

node.js

uncaught-exception

express