问题描述
在 node.js 中 readFile() 显示了如何捕获错误，但是没有对readFileSync() 函数关于错误处理.因此，如果我在没有文件时尝试使用 readFileSync()，则会收到错误 Error: ENOENT, no such file or directory.
Within node.js readFile() shows how to capture an error, however there is no comment for the readFileSync() function regarding error handling. As such, if I try to use readFileSync() when there is no file, I get the error Error: ENOENT, no such file or directory.
如何捕获抛出的异常?doco 没有说明抛出什么异常，所以我不知道我需要捕获什么异常.我应该注意，我不喜欢 try/catch 语句的通用捕获每个可能的异常"样式.在这种情况下，我希望捕获在文件不存在时发生的特定异常，并且我尝试执行 readFileSync.
How do I capture the exception being thrown? The doco doesn't state what exceptions are thrown, so I don't know what exceptions I need to catch. I should note that I don't like generic 'catch every single possible exception' style of try/catch statements. In this case I wish to catch the specific exception that occurs when the file doesn't exist and I attempt to perform the readFileSync.
请注意，我仅在启动连接尝试之前执行同步功能，因此不需要我不应该使用同步功能的评论:-)
Please note that I'm performing sync functions only on start up before serving connection attempts, so comments that I shouldn't be using sync functions are not required :-)
推荐答案
基本上，fs.readFileSync 在找不到文件时会抛出错误.此错误来自 Error 原型并使用 throw 抛出，因此捕获的唯一方法是使用 try/catch 块:
Basically, fs.readFileSync throws an error when a file is not found. This error is from the Error prototype and thrown using throw, hence the only way to catch is with a try / catch block:
var fileContents;
try {
fileContents = fs.readFileSync('foo.bar');
} catch (err) {
// Here you get the error when the file was not found,
// but you also get any other error
}
不幸的是，您无法仅通过查看其原型链来检测抛出了哪个错误:
Unfortunately you can not detect which error has been thrown just by looking at its prototype chain:
if (err instanceof Error)
是你能做的最好的，这对于大多数(如果不是全部)错误都是正确的.因此，我建议您使用 code 属性并检查其值:
is the best you can do, and this will be true for most (if not all) errors. Hence I'd suggest you go with the code property and check its value:
if (err.code === 'ENOENT') {
console.log('File not found!');
} else {
throw err;
}
这样，您只处理这个特定错误并重新抛出所有其他错误.
This way, you deal only with this specific error and re-throw all other errors.
或者，您也可以访问错误的 message 属性来验证详细的错误消息，在本例中为:
Alternatively, you can also access the error's message property to verify the detailed error message, which in this case is:
ENOENT, no such file or directory 'foo.bar'
希望这会有所帮助.
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