fs.exists(path, callback)

• path <string> | <Buffer> | <URL>

• callback <Function>

  • exists <boolean>

通过检查文件系统来测试给定的路径是否存在。然后使用 true 或 false 调用 callback 参数：

¥Test whether or not the given path exists by checking with the file system. Then call the callback argument with either true or false:

import { exists } from 'node:fs';

exists('/etc/passwd', (e) => {
  console.log(e ? 'it exists' : 'no passwd!');
}); 拷贝

此回调的参数与其他 Node.js 回调不一致。通常，Node.js 回调的第一个参数是 err 参数，后面可以选择其他参数。fs.exists() 回调只有一个布尔参数。这是推荐 fs.access() 而不是 fs.exists() 的原因之一。

¥The parameters for this callback are not consistent with other Node.js callbacks. Normally, the first parameter to a Node.js callback is an err parameter, optionally followed by other parameters. The fs.exists() callback has only one boolean parameter. This is one reason fs.access() is recommended instead of fs.exists().

不建议在调用 fs.open()、fs.readFile() 或 fs.writeFile() 之前使用 fs.exists() 检查文件是否存在。这样做会引入竞争条件，因为其他进程可能会在两次调用之间更改文件的状态。而是，用户代码应该直接打开/读取/写入文件，并在文件不存在时处理引发的错误。

¥Using fs.exists() to check for the existence of a file before calling fs.open(), fs.readFile(), or fs.writeFile() is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file does not exist.

写入（不推荐）

¥write (NOT RECOMMENDED)

import { exists, open, close } from 'node:fs';

exists('myfile', (e) => {
  if (e) {
    console.error('myfile already exists');
  } else {
    open('myfile', 'wx', (err, fd) => {
      if (err) throw err;

      try {
        writeMyData(fd);
      } finally {
        close(fd, (err) => {
          if (err) throw err;
        });
      }
    });
  }
}); 拷贝

写入（推荐）

¥write (RECOMMENDED)

import { open, close } from 'node:fs';
open('myfile', 'wx', (err, fd) => {
  if (err) {
    if (err.code === 'EEXIST') {
      console.error('myfile already exists');
      return;
    }

    throw err;
  }

  try {
    writeMyData(fd);
  } finally {
    close(fd, (err) => {
      if (err) throw err;
    });
  }
}); 拷贝

读取（不推荐）

¥read (NOT RECOMMENDED)

import { open, close, exists } from 'node:fs';

exists('myfile', (e) => {
  if (e) {
    open('myfile', 'r', (err, fd) => {
      if (err) throw err;

      try {
        readMyData(fd);
      } finally {
        close(fd, (err) => {
          if (err) throw err;
        });
      }
    });
  } else {
    console.error('myfile does not exist');
  }
}); 拷贝

读取（推荐）

¥read (RECOMMENDED)

import { open, close } from 'node:fs';

open('myfile', 'r', (err, fd) => {
  if (err) {
    if (err.code === 'ENOENT') {
      console.error('myfile does not exist');
      return;
    }

    throw err;
  }

  try {
    readMyData(fd);
  } finally {
    close(fd, (err) => {
      if (err) throw err;
    });
  }
}); 拷贝

上面的 "不建议" 示例检查文件是否存在，然后使用该文件；"recommended" 示例更好，因为它们直接使用文件并处理错误（如果有）。

¥The "not recommended" examples above check for existence and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.

一般来说，只有在文件不被直接使用时才检查文件是否存在，例如当它的存在是来自另一个进程的信号时。

¥In general, check for the existence of a file only if the file won't be used directly, for example when its existence is a signal from another process.