Quick review: Use of the FS module in Node.js

JavaScript does not have the ability to manipulate files, but Node does. Node provides the file system module, which is very important and frequently used in Node. It is definitely a module system to master.

Fs module provides a lot of interfaces, here is mainly to say some commonly used interfaces.

1. Quick review of common apis

fs.statCheck whether it is a file or a directory

const fs = require('fs')
fs.stat('hello.js'.(error,stats) = >{
    if(error) {
        console.log(error)
    } else {
        console.log(stats)
        console.log(` file:${stats.isFile()}`)
        console.log(` directory:${stats.isDirectory()}`)}})Copy the code

fs.mkdirCreate a directory

const fs = require('fs')
fs.mkdir('logs'.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Directory created successfully! ')}})Copy the code

fs.rmdirDelete the directory

const fs = require('fs')
fs.rmdir('logs'.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Directory logs were deleted successfully')}})Copy the code

fs.writeFileCreate write file

const fs = require('fs')
fs.writeFile('logs/hello.log'.'hello ~ \ n'.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Write file successfully'); }})Copy the code

fs.appendFileAdditional documents

const fs = require('fs')
fs.appendFile('logs/hello.log'.'hello~\n'.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Write file successfully'); }})Copy the code

fs.readFileRead the file

const fs = require('fs')
fs.readFile('logs/hello.log'.'utf-8'.(error, data) = > {
    if(error) {
        console.log(error)
    } else {
        console.log(data); }})Copy the code

fs.unlinkDelete the file

const fs = require('fs')
fs.unlink(`logs/${file}`.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Successfully deleted file:${file}`)}})Copy the code

fs.readdirRead the directory

const fs = require('fs')
fs.readdir('logs'.(error, files) = > {
    if(error) {
        console.log(error)
    } else {
        console.log(files); }})Copy the code

fs.renameRename, you can also change the file storage path

const fs = require('fs')
fs.rename('js/hello.log'.'js/greeting.log'.error= > {
    if(error) {
        console.log(error)
    } else {
        console.log('Rename successful')}})Copy the code

2. Use of the third-party NPM package mkdirp

You can run the mkdirp command to create not only folders but also multilayer folders

midir -p tmp/foo/bar/baz
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The above command can also create multiple folders in the current directory.

The following code generates multi-level folders in the current directory

const mkdirp = require('mkdirp')

mkdirp('tmp/foo/bar/baz').then(made= > console.log('create directory at:${made}`))

/ / create the directory: / Users/zhangbing/lot/CodeTest/Node/fs/TMP
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The results of

3. Practical examples

Practice 1

Check whether there is an Upload directory on the server. If not, create the directory; if not, do nothing

const fs = require('fs')

const path = './upload'
fs.stat(path, (err, data) = > {
    if(err) {
        // Create a directory
        mkdir(path)
        return
    }
    if(data.isDirectory()) {
        console.log('Upload directory exists');
    }else{
        // Delete the file before creating the directory
        fs.unlink(path, err= > {
            if(! err) { mkdir(path) } }) } })function mkdir(dir) {
    fs.mkdir(dir, err= > {
        if(err) {
            console.log(err);
            return}})}Copy the code

Actual combat 2

Under the wwwroot folder are images CSS JS and index.html. Find all the directories under the wwwroot directory and place them in an array

Use the synchronous method approach

const fs = require('fs')
const path = './wwwroot'
const dirArr = []

const dirs = fs.readdirSync(path)
dirs.forEach(item= > {
    if(fs.statSync(path + '/' + item).isDirectory()) {
        dirArr.push(item)
    }
})
console.log('dirArr', dirArr)
// dirArr [ 'css', 'images', 'js' ]
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Use async/await mode

const fs = require('fs')
const path = './wwwroot'
const dirArr = []

function isDir(path) {
    return new Promise((resolve, reject) = > {
        fs.stat(path, (error, stats) = > {
            if(error) {
                console.log(error)
                reject(error)
                return
            }
            if(stats.isDirectory()) {
                resolve(true)}else {
                resolve(false)}})})}function main(){
    fs.readdir(path, async (error, data) => {
        if(error) {
            console.log(error)
            return
        } else {
            for(let i = 0; i < data.length; i++) {
                if(await isDir(path + '/' + data[i])) {
                    dirArr.push(data[i])
                }
            }
            console.log('dirArr', dirArr)
        }
    })
}

main() // dirArr [ 'css', 'images', 'js' ]
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4. The pipe flow

Pipes provide a mechanism for an output stream to an input stream. Typically we use it to get data from one stream and pass it to another stream. In the following example, we read the contents of one file and write the contents to another file.

const fs = require("fs")
// Create a readable stream
const readerStream = fs.createReadStream('input.txt')
// Create a writable stream
const writerStream = fs.createWriteStream('output.txt')
// Pipe read and write operations
// Read the contents of input. TXT and write the contents to output. TXT
readerStream.pipe(writerStream)
console.log("Program completed")
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fs.createReadStreamReads data from a file stream

const fs = require('fs')
const fileReadStream = fs.fileReadStream('demo1.js')
let count = 0
let str = ' '
fileReadStream.on('data'.chunk= > {
    console.log(`${++count}To receive:${chunk.length}`)
    str += chunk
})
fileReadStream.on('end'.() = > {
    console.log('end -- -- -- -- -- --)
    console.log(count + ', ' + star)
})
fileReadStream.on('error'.error= > {
    console.log(error)
})
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fs.createWriteStreamWritten to the file

const fs = require("fs")
const data ='I'm getting the data from the database, I'm going to save it.'
// Create a stream that can be written to the file output.txt
const writerStream = fs.createWriteStream('output.txt')
// Write data using UTF8 encoding
writerStream.write(data,'UTF8')
// Mark the end of the file
writerStream.end()
// Process the stream event --> Finish event
writerStream.on('finish'.() = > {
    /* Finish - Triggered when all data has been written to the underlying system. * /
    console.log("Write complete.")
})
writerStream.on('error'.err= > {
    console.log(err.stack);
})
console.log("Program completed")
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Practice: Copy pictures

There is an image 2020.png in the project root directory. Copy it to /wwwroot/images

The following code

const fs = require("fs")

const readStream = fs.createReadStream('./2020.png')
const writeStream = fs.createWriteStream('./wwwroot/images/2021.png')

readStream.pipe(writeStream)
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Fs.createwritestream (‘./wwwroot/images/’) : fs.createWritestream (‘./wwwroot/images/’) : fs.createWritestream (‘./wwwroot/images/’) : fs.createWritestream (‘./wwwroot/images/’)

Error: EISDIR: illegal operation on a directory, open <directory>
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Source: github.com/dunizb/Code…

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