nodejs copy file

js

const fs = require("fs");
const util = require('util');
const path = require('path');
const source = path.resolve(".", "src/1.mp4")
const target = path.resolve(".", "src/bak.mp4")

let postion = 0;
let list = [];

fs.open(source, "r", function (err, fr) {
  function rea() {
    let buffer = Buffer.alloc(4096);
    fs.read(fr, buffer, 0, 4096, postion, function (err, bytesRead) {
      if (bytesRead > 0) {
        let temp = buffer.slice(0, bytesRead)
        fs.open(target,"a",function(err,fw){
         fs.write(fw,temp,0,bytesRead,postion,function(err,byteswrite){
            postion += bytesRead
            rea()
         })
        })
      } 
    })
  }
  rea()

});