How to use the fs method of nodejs

Node.js is a JavaScript running environment based on the Chrome V8 engine. It can run JavaScript code on the server side and handle high-concurrency, I/O-intensive applications. Node.js provides many built-in modules, including the file system module (fs). The fs module provides many methods for reading, writing, and manipulating files.

In this article, we will introduce the method of Node.js’s fs module. We'll explain what each method does and uses, and how to use them to process files.

1. fs.open()

The fs.open() method is used to open files in Node.js. The syntax of this method is as follows:

fs.open(path, flags[, mode], callback)

Parameter description:

• path: The path of the file to be opened.
• flags: Flags for the operation to be performed. Optional parameter, default is 'w'.
• mode: Set file mode (permissions and default interface). Optional parameter, default is 0666.
• callback: callback function, parameters are (err, fd).

The flags parameter is a string indicating the operation mode. Some commonly used flags are listed below:

• r: Open the file in read mode. If the file does not exist, an exception occurs.
• r : Open the file in read and write mode. If the file does not exist, an exception occurs.
• w: Open the file in writing mode. If the file does not exist, a new file is created. If the file exists, deletes all data contained in the file.
• w : Open the file in read and write mode. If the file does not exist, a new file is created. If the file exists, deletes all data contained in the file.
• a: Open the file in append mode. If the file does not exist, a new file is created.
• a : Open the file in read and append mode. If the file does not exist, a new file is created.

Example:

const fs = require('fs');
fs.open('test.txt', 'w', function (err, fd) {
  if (err) {
    throw err;
  }
  console.log('文件已打开!');
});

2. fs.readFile()

fs.readFile() method is used to read in Node.js document. The syntax of this method is as follows:

fs.readFile(path[, options], callback)

Parameter description:

• path: The path of the file to be read.
• options: Object or string specifying the encoding and flags of the file (default is 'utf8').
• callback: callback function, parameters are (err, data).

Example:

const fs = require('fs');
fs.readFile('test.txt', function (err, data) {
  if (err) {
    throw err;
  }
  console.log(data.toString());
});

3. fs.writeFile()

fs.writeFile() method is used to write in Node.js document. The syntax of this method is as follows:

fs.writeFile(file, data[, options], callback)

Parameter description:

• file: The path of the file to be written.
• data: The data to be written to the file.
• options: Object or string specifying the encoding and flags of the file (default is 'utf8').
• callback: callback function, parameter is (err).

Example:

const fs = require('fs');
fs.writeFile('test.txt', 'Hello Node.js!', function (err) {
  if (err) {
    throw err;
  }
  console.log('文件已保存!');
});

4. fs.appendFile()

The fs.appendFile() method is used to append data in Node.js to file. The syntax of this method is as follows:

fs.appendFile(file, data[, options], callback)

Parameter description:

• file: The path of the file to be written.
• data: The data to be written to the file.
• options: Object or string specifying the encoding and flags of the file (default is 'utf8').
• callback: callback function, parameter is (err).

Example:

const fs = require('fs');
fs.appendFile('test.txt', 'Hello again!', function (err) {
  if (err) {
    throw err;
  }
  console.log('数据已追加到文件!');
});

5. fs.unlink()

fs.unlink() method is used to delete files in Node.js . The syntax of this method is as follows:

fs.unlink(path, callback)

Parameter description:

• path: The path of the file to be deleted.
• callback: callback function, parameter is (err).

Example:

const fs = require('fs');
fs.unlink('test.txt', function (err) {
  if (err) {
    throw err;
  }
  console.log('文件已删除!');
});

6.fs.rename()

The fs.rename() method is used to rename files in Node.js. The syntax of this method is as follows:

fs.rename(oldPath, newPath, callback)

Parameter description:

• oldPath: The old path of the file to be renamed.
• newPath: The new path of the file to be renamed.
• callback: callback function, parameter is (err).

Example:

const fs = require('fs');
fs.rename('test.txt', 'newTest.txt', function (err) {
  if (err) {
    throw err;
  }
  console.log('文件已重命名!');
});

Summary

In Node.js, the fs module provides many methods for reading, writing, and manipulating files. Use these methods to conveniently handle file system operations. This article introduces commonly used fs methods and provides practical examples. I hope this article can help you better understand the use of Node.js’s fs module.

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