Talk about file writing in Node.js

This article will introduce you to file writing inNode.js. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

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It is very simple to read the file and then read the file writing , the operations of the two correspond almost one-to-one

fs.writeFile

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

• file: file name or file descriptor

• data: the most commonly used ones are string and buffer

• callback(err)

Whenfileis a file name, write data to the file asynchronously. If the file already exists,overwrite the file content

const fs = require('fs'); const data = Buffer.from('Hello, Node.js'); fs.writeFile('./test.txt', data, err => { if (err) throw err; console.log('文件已被保存'); });

fs.write

fs.write has two overloads

• fs.write(fd, buffer[, offset[ , length[, position]]], callback): The parameter meaning is almost the same as fs.read

• fs.write(fd, string[, position[, encoding]], callback) : Only the entire string content can be written to the file

The difference between the two is that using buffer can write the contents ofoffset ~ length offsetin the buffer, while Using strings can only write the entire string content to the file

const fs = require('fs'); const data1 = Buffer.from('Hello, Node.js'); const data2 = 'Hello, Node.js'; const fd = fs.openSync('./test.txt', 'w'); console.log(fd) fs.write(fd, data1, err => { if (err) throw err; console.log('data1 已被写入'); }); fs.write(fd, data2, err => { if (err) throw err; console.log('data2 已被写入'); }); setTimeout(() => { fs.close(fd, console.log); }, 100);

fs.appendFile

fs.appendFile(path, data[, options], callback)will Data is appended to the end of the file. If the file does not exist, the file is created

const fs = require('fs/promises'); const data1 = Buffer.from('Hello,'); const data2 = Buffer.from(' Node.js'); fs.appendFile('./test.txt', data1) .then(() => { fs.appendFile('./test.txt', data2); console.log('文件内容追加完成'); });

fs.createWriteStream

fs.createWriteStream(path[, options])Used to create a Writable file stream, options are almost the same as fs.createReadStream
options (the more commonly used ones are)

• fd: The default value is null, if fd is specified, the path parameter will be ignored, use The specified file descriptor (the open event will not be triggered again)
• mode: Default value 0o666
• autoClose: Default value: true, when the 'error' or 'finish' event occurs, the file description The symbol will be automatically closed
• start: The position where writing to the file starts, no default override is set

Writing the contents of a readable stream to a writable stream is very simple

const fs = require('fs'); fs.createReadStream('./test.txt') .pipe(fs.createWriteStream('./copy.txt'));

The introduction and more uses of streams will be introduced in detail in the Buffer and Stream chapters

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