如何捕获fs.readFileSync（）的文件？ [英] How to capture no file for fs.readFileSync()?

问题描述

在node.js中 readFile（）显示了如何捕获错误，但是没有任何评论有关错误处理的 readFileSync（）功能。因此，如果我没有文件时尝试使用readFileSync（），我会收到错误错误：ENOENT，没有这样的文件或目录。

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？该doco没有说明抛出什么异常，所以我不知道什么异常我需要抓住。我应该注意到，我不喜欢通用的'catch每一个可能的异常'风格的try / catch语句。在这种情况下，我希望捕获该文件不存在时发生的特定异常，并尝试执行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，我正在执行同步仅在启动连接尝试之前才起作用，所以不需要使用同步功能的注释:-)

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

p>基本上， fs.readFileSync 在找不到文件时会引发错误。这个错误来自错误原型并使用 throw 抛出，因此唯一的方法是使用 try / catch block：

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，您无法通过查看其原型链来检测哪些错误被抛出：

Unfortunately you can not detect which error has been thrown just by looking at its prototype chain:

if (err instanceof Error)

是你可以做的最好的，这对大多数（如果不是全部）错误将是正确的。因此，我建议您使用代码属性并检查其值：

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，你只处理这个特定错误，并重新抛出所有其他

This way, you deal only with this specific error and re-throw all other errors.

或者，您还可以访问错误的消息属性来验证详细的错误消息，在此情况是：

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'

希望这有帮助。

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