This article uses the case of reading and writing files and processing paths to learn about the fs file module and path module in Node. I hope it will be helpful to everyone!

1. fs file system module

fs module is Node. js Officially provided module for manipulating files. It provides a series of methods and properties to meet user requirements for file operations. [Related tutorial recommendations: nodejs video tutorial]

1. Read the specified file

##fs. readFile(): Read the contents of the specified file

Parameter 1: Required parameter, string, indicating the path of the file

Parameter 2: Optional parameter, indicating what Encoding format to read the file
Parameter 3: Required parameter. After the file reading is completed, the read result is obtained through the callback function

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

Example 1: Read demo.txt file

##demo.txt file

'前端雜貨鋪'

app.js File

// 導入 fs 文件系統(tǒng)模塊
const fs = require('fs')

// 讀取文件 utf-8 為中文編碼格式
fs.readFile('../files/demo.txt', 'utf-8', function (err, data) {
    console.log('err：', err)
    console.log('data：', data)
})

Note: If you write the wrong path, that is, the file reading fails, the printed content is as follows [err is the error object, data is undefined]

Example 2: Determine whether reading the demo.txt file is successful

app.js file

Intentional wrong path, reading failed

• The failure result is as follows

• // 導入 fs 模塊
  const fs = require('fs')
  
  // 讀取文件
  fs.readFile('../files/demo1.txt', 'utf-8', function (err, data) {
      if(err) {
          return console.log('讀取文件失敗', err.message)
      }
      console.log('data：', data)
  })

2. Write the specified file

fs.writeFile(): Write content to the specified file

Parameter 1: Required parameter, you need to specify a string of file path, indicating the storage path of the file

Parameter 2: Required parameter, indicating the content to be written

Parameter 3: Yes Select the parameter to indicate the format in which the file content is written. The default is utf-8
Parameter 4: Required parameter, the callback function after the file writing is completed

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

Example 1: Write demo.txt file

##demo.txt file

// 該文件內(nèi)容為空

app.js file

// 導入 fs 文件系統(tǒng)模塊
const fs = require('fs')

// 寫入文件內(nèi)容
fs.writeFile('../files/demo.txt', '這里是前端雜貨鋪', function(err, data) {
    if (err) {
        return console.log('寫入文件失敗', err.message)
    }
    console.log('文件寫入成功')
})

Note: If writing to a disk that does not exist, the file writing fails and the printed content is as follows

3. Cases of organizing resultsExample: format conversion of results

Grade format before conversion

Grade format after conversion

The file format is as follows

score.txt file

Write the score Content

雜貨鋪=100 張三=98 李四=95 王五=92

app.js file

Import the required fs file module

Use the fs.readFile() method, Read the score.txt file in the material directory
Determine whether the file reading fails
After the file is read successfully, process the score data
The completed score data will be processed. Call the fs.writeFile() method to write to the new file newScore.txt

// 導入 fs 文件系統(tǒng)模塊
const fs = require('fs')

// 寫入文件內(nèi)容
fs.readFile('../files/score.txt', 'utf-8', function (err, data) {
    // 判斷是否讀取成功
    if (err) {
        return console.log('讀取文件失敗' + err.message)
    }
    // 把成績按空格進行分割
    const arrOld = data.split(' ')
    // 新數(shù)組的存放
    const arrNew = []
    // 循環(huán)分割后的數(shù)組 對每一項數(shù)據(jù) 進行字符串的替換操作
    arrOld.forEach(item => {
        arrNew.push(item.replace('=', '：'))
    })
    // 把新數(shù)組中的每一項合并 得到新的字符串
    const newStr = arrNew.join('\r\n')

    // 寫入新數(shù)據(jù)
    fs.writeFile('../files/newScore.txt', newStr, function (err) {
        if (err) {
            return console.log('寫入成績失敗' + err.message)
        }
        console.log('成績寫入成功')
    })
})

##4. Processing path

__dirname: Indicates the directory where the current file is located

Example: Write relative path

const fs = require('fs')

fs.readFile('../files/score.txt', 'utf-8', function(err, data) {
    if (err) {
        return console.log('文件讀取失敗' + err.message)
    }
    console.log('文件讀取成功')
})

示例：使用 __dirname

const fs = require('fs')

// 讀取文件
fs.readFile(__dirname + '/files/score.txt', 'utf-8', function(err, data) {
    if (err) {
        return console.log('文件讀取失敗' + err.message)
    }
    console.log('文件讀取成功')
})

二、path 路徑模塊

path 模塊是 Node.js 官方提供的、用來處理路徑的模塊

1、path.join() 路徑拼接

path.join()：用來將多個路徑判斷拼接成一個完整的路徑字符串

參數(shù)：…paths <string> 路徑片段的序列
返回值：返回值 <string>

path.join([...paths])

示例：路徑拼接

// 導入 path 模塊
const path = require('path')
// ../ 會抵消前面的路徑
const pathStr = path.join('/a','/b/c', '../', './d', 'e')
console.log(pathStr)

備注：涉及到路徑拼接的操作，都要使用 path.join() 方法進行處理。不要直接用 + 進行字符串拼接

示例：使用 path 進行路徑拼接

const fs = require('fs')
const path = require('path')

// 文件讀取
fs.readFile(path.join(__dirname, '/files/score.txt'), 'utf-8', function(err, data) {
    if (err) {
        return console.log('文件讀取失敗', err.message)
    }
    console.log('文件讀取成功')
})

2、path.basename() 解析文件名

path.basename()：用來從路徑字符串中，將文件名解析出來

參數(shù) 1：path 必選參數(shù)，表示一個路徑的字符串
參數(shù) 2：ext 可選參數(shù)，表達文件擴展名
返回值：返回 表示路徑中的最后一部分

path.basename(path, [ext])

示例：解析路徑，去除擴展名

// 導入 path 模塊
const path = require('path')
// 文件的存放路徑
const fpath = '/a/b/c/index.html'

// 將文件名解析出來
const fullName = path.basename(fpath)
console.log(fullName) // 輸出 index.html

// 去除擴展名
const nameWithoutExt = path.basename(fpath, '.html')

console.log(nameWithoutExt) // 輸出 index

3、path.extname() 獲取擴展名

path.extname()：可以獲取路徑中的擴展名部分

參數(shù)：path <string> 必選參數(shù)，表示一個路徑的字符串
返回值：返回 <string> 返回得到的擴展名字符串

path.extname(path)

示例：獲取擴展名

// 導入 path 模塊
const path = require('path')
// 文件的存放路徑
const fpath = '/a/b/c/index.html'
// 獲取擴展名
const fext = path.extname(fpath)

console.log(fext) // .html

更多node相關(guān)知識，請訪問：nodejs 教程！

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