Does the nodejs file exist?

In Node.js, we often need to determine whether a file exists. This is a common requirement. For example, before reading a file, you need to determine whether the file exists. Otherwise, some unnecessary errors may occur.

So, how to determine whether a file exists in Node.js? We can use the fs.access() method in the fs module to achieve this function. The fs.access() method is used to determine the permissions of a file or directory. If the file or directory exists, the callback function will not throw an error.

Code example:

const fs = require('fs');

fs.access('/path/to/file', fs.constants.F_OK, (err) => {
  if (err) {
    console.error('文件不存在');
  } else {
    console.log('文件存在');
  }
});

In the above code, we called the fs.access() method and passed in the following parameters:

• /path/to/file: The file path to determine whether it exists.
• fs.constants.F_OK: Indicates to determine whether the file exists.

If the file exists, the callback function will not throw an error, and we can perform the required operations in the callback function. Otherwise, the callback function will throw an ENOENT error. We can capture this error in the callback function and handle it accordingly, such as outputting error information.

In actual development, we may need to determine whether a directory exists. Similar to the method of determining whether a file exists, we only need to use the fs.constants.R_OK constant to indicate whether the directory exists.

Code example:

const fs = require('fs');

fs.access('/path/to/dir', fs.constants.R_OK, (err) => {
  if (err) {
    console.error('目录不存在');
  } else {
    console.log('目录存在');
  }
});

The above is a method to use the fs.access() method to determine whether a file or directory exists. Of course, there are other methods, such as using the fs.stat() method.

Code example:

const fs = require('fs');

fs.stat('/path/to/file', (err, stats) => {
  if (err) {
    console.error('文件不存在');
  } else {
    console.log('文件存在');
  }
});

In the above code, we call the fs.stat() method, which can return status information about the file or directory, including file size and modification time wait. If the file or directory exists, the callback function will not throw an error.

Summary

The above are two ways to determine whether a file or directory exists. We can choose to use the fs.access() method or the fs.stat() method according to the actual situation. No matter which method is used, when determining whether a file or directory exists, we need to pay attention to the following points:

• The path should be an absolute path.
• In different operating systems, the path separator may be different (for example, it is in Windows, but it is / in Linux and macOS), and we need to pay attention to the distinction.

I hope this article is helpful to you. If you have any questions, please leave a message in the comment area and we will reply in time.

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