通过4中不通的方式实现对一个文件的拷贝

方式一：readFile 异步一次性读取文件再写入

//异步形式读取文件function copyFile(url){    const extName = path.extname(url)    const fileName = path.basename(url)    const dirName = path.dirname(url)    fs.readFile(url, (err, data) => {        fs.writeFile(`${dirName}/${fileName}_copy_1${extName}`, data , err => {            if(err){                console.log(`写入出现错误 ${err.toString()}`)            }else{                console.log('完成!')            }        })    })}

方式二：readFileSync 同步一次性读取文件再写入

//同步形式读取文件function copySync(url){    const extName = path.extname(url)    const fileName = path.basename(url)    const dirName = path.dirname(url)    var data = fs.readFileSync(url)        fs.writeFileSync(`${dirName}/${fileName}_copy_1${extName}`,data)    console.log('同步拷贝完成!')}

方式三：使用流边读边写

const fs = require('fs')const path = require('path')// 使用流拷贝function streamCopyFile(url){    const extName = path.extname(url)    const fileName = path.basename(url)    const dirName = path.dirname(url)    let options = {        highWaterMark : 64 * 1024 //默认值，每个chunk的大小    }    const readable = fs.createReadStream(url, options)    const writable = fs.createWriteStream(`${dirName}/${fileName}_copy${extName}`)    var size = 0    var totalSize = 0    const stat = fs.stat(url, (err , stats) => {        totalSize = stats.size    })    readable.on('open', () => {        console.log('打开文件');    })    readable.on('data', data => {        size = data.length + size        console.log('已完成 ' + parseInt((size / totalSize) * 100) + '%');        writable.write(data)        readable.pause()    })    readable.on('end', () => {        console.log('读取完成')    })    readable.on('error', err => {        console.log(`读取时出现错误 ${err.toString()}`)    })    writable.on('error', err => {        console.log(`写入时出现错误 ${err.toString()}`)    })    //将内存中数据全部写入文件后触发 drain 事件    writable.on('drain', () => {        readable.resume()    })    writable.on('finish', () => {        console.error('写入完成');    })}

方式四：使用pipe

//通过管道的方式function pipeCopyFile(url){    const extName = path.extname(url)    const fileName = path.basename(url)    const dirName = path.dirname(url)    const readable = fs.createReadStream(url)    const writable = fs.createWriteStream(`${dirName}/${fileName}_copy_2${extName}`)    var size = 0    var totalSize = 0    const stat = fs.stat(url, (err , stats) => {        totalSize = stats.size    })    writable.on('pipe', (src) => {        console.log('有数据正通过管道流入写入器')    })    writable.on('finish', () => {        console.error('写入已完成')    })    readable.pipe(writable)}

方法一和方法二使用起来简单，但是在操作大文件时对内存压力大，不推荐读取大文件使用

另外如果需要对文件制定块进行读取和写入请使用read 、write 两个方法