Javascript 如何正确处理 Express 中的错误？
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How to properly handle errors in Express?
提问by YWCA Hello
I am beginning to work with Express JS and have run into an issue. I can't seem to figure out the proper way to handle errors.
我开始使用 Express JS 并遇到了一个问题。我似乎无法找出处理错误的正确方法。
For example, I have a web services API that serves an object called "event". I'd like to return a simple string of "cannot find event" when a user submits an event id that isn't found. Here is how I'm currently structuring my code:
例如，我有一个 Web 服务 API，它为一个名为“事件”的对象提供服务。当用户提交未找到的事件 ID 时，我想返回一个简单的“找不到事件”字符串。这是我目前构建代码的方式：
app.get('/event/:id', function(req, res, next) {
if (req.params.id != 1) {
next(new Error('cannot find event ' + req.params.id));
}
req.send('event found!');
});
When I submit an idother than 1, Node crashes with the following output:
当我提交1 以外的id 时，Node 崩溃并显示以下输出：
http.js:527
throw new Error("Can't set headers after they are sent.");
^
Error: Can't set headers after they are sent.
at ServerResponse.<anonymous> (http.js:527:11)
at ServerResponse.setHeader (/usr/local/kayak/node_modules/express/node_modules/connect/lib/patch.js:62:20)
at /usr/local/kayak/node_modules/express/node_modules/connect/lib/middleware/errorHandler.js:72:19
at [object Object].<anonymous> (fs.js:107:5)
at [object Object].emit (events.js:61:17)
at afterRead (fs.js:878:12)
at wrapper (fs.js:245:17)
From what I can tell by using the node.js debugger, execution of the block of code continues after next()is called, meaning that req.send('event found!')tries to run. I don't want this to happen.
从我使用 node.js调试器可以看出，代码块的执行在next()被调用后继续执行，这意味着它会req.send('event found!')尝试运行。我不希望这种情况发生。
The only workaround that I've found is to simply throw a new Error()instead of "next-ing" it, but this results in a default Express HTML error page being generated. I'd like a little more control than that.
我发现的唯一解决方法是简单地抛出一个new Error()而不是“next-ing”它，但这会导致生成默认的 Express HTML 错误页面。我想要更多的控制权。
I have taken the time to read over the error handling sectionof the Express documentation, but I couldn't make sense of it.
我花时间阅读了Express 文档的错误处理部分，但我无法理解。
回答by Chance
You'll want to check out Express Error Handling. From there:
您需要查看Express Error Handling。从那里：
app.param('userId', function(req, res, next, id) {
User.get(id, function(err, user) {
if (err) return next(err);
if (!user) return next(new Error('failed to find user'));
req.user = user;
next();
});
});
The sweetspot that you are missing is the returnnext(...)
你缺少的甜蜜点是 returnnext(...)
回答by alessioalex
That's because you're doing it wrong: you already threw an Error (which will be processed by Express and return a 500 - Error page for the user or something like that) but you are also trying to send your own response to the client: res.send('event found!');
那是因为你做错了：你已经抛出了一个错误（它将被 Express 处理并为用户返回一个 500 - 错误页面或类似的页面）但你也试图将自己的响应发送给客户端： res.send('找到事件！');
You should really check out the Express guide about Error Handling here: http://expressjs.com/guide/error-handling.html
你真的应该在这里查看关于错误处理的 Express 指南：http: //expressjs.com/guide/error-handling.html
What I would do in your example is:
我在你的例子中会做的是：
function NotFound(msg){
this.name = 'NotFound';
Error.call(this, msg);
Error.captureStackTrace(this, arguments.callee);
}
app.get('/event/:id', function(req, res, next){
if (req.params.id != 1) {
throw new NotFound('Cannot find event ' + req.params.id);
} else {
res.send('event found!');
}
});
app.error(function(err, req, res, next){
if (err instanceof NotFound) {
res.render('404.ejs');
} else {
next(err);
}
});
回答by evilcelery
You have a couple of problems in your code:
您的代码中有几个问题：
When responding to the client, you need to use the responseobject(
resrather thanreq).When sending an error to
next, you should return, so the rest of the function doesn't run.
响应客户端时，需要使用响应对象（
res而不是req）。向 发送错误时
next，您应该返回，因此函数的其余部分不会运行。
Here's your code after fixing those errors:
这是修复这些错误后的代码：
app.get('/event/:id', function(req, res, next) {
if (req.params.id != 1) {
return next(new Error('cannot find event ' + req.params.id));
}
res.send('event found!'); // use res.send (NOT req.send)
});
