How to detect whether a file exists in nodejs

Detection method: 1. Use "fs.exists(path,callback)"; 2. Use "await util.promisify(fs.stat)('file path')"; 3. Use "fs. access(path[,mode],callback);".

The operating environment of this tutorial: windows7 system, nodejs version 14.15.4, DELL G3 computer.

Nodejs method to detect whether a file exists:

1. Use fs.exists

The exists() function can test whether a file under a certain path exists. Syntax format:

fs.exists(path, callback)

• path file path to be detected

• callback callback

  • callback function Contains a parameter exists, true if the file exists, otherwise false.

Note: Since this method belongs to the fs module, the fs module needs to be introduced before use (var fs= require(“fs”) )

Currently fs.exists has been abandoned. In addition, it needs to be clear that the file exists only when it is not used directly.

Example:

fs.exists('/etc/passwd', function (exists) {
  util.debug(exists ? "it's there" : "no passwd!");
});

2. Use fs.stat

fs.stat returns a fs.Stats object, which provides a lot of information about the file, such as file size, creation time, etc. There are two methods, stats.isDirectory() and stats.isFile(), which are used to determine whether it is a directory or a file.

const stats = await util.promisify(fs.stat)('text1.txt'); 
console.log(stats.isDirectory()); // false 
console.log(stats.isFile()); // true

If you just check whether the file exists, it is recommended to use the following fs.access.

3. Use fs.access

fs.access receives a mode parameter to determine whether a file exists, is readable, and writable. The return value is a err parameter.

const file = 'text.txt'; // 检查文件是否存在于当前目录中。
fs.access(file, fs.constants.F_OK, (err) => {
 console.log(`${file} ${err ? '不存在' : '存在'}`);
}); // 检查文件是否可读。
fs.access(file, fs.constants.R_OK, (err) => {
 console.log(`${file} ${err ? '不可读' : '可读'}`); 
}); // 检查文件是否可写。 
fs.access(file, fs.constants.W_OK, (err) => {
 console.log(`${file} ${err ? '不可写' : '可写'}`);
 }); // 检查文件是否存在于当前目录中、以及是否可写。
fs.access(file, fs.constants.F_OK | fs.constants.W_OK, (err) => {
 if (err) {
  console.error( `${file} ${err.code === 'ENOENT' ? '不存在' : '只可读'}`); 
  } else { 
  console.log(`${file} 存在，且可写`); 
  } 
});

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