【每日一包0021】csv2,through2

[github地址：https://github.com/ABCDdouyae...]

csv2

採用流模式讀取.csv文件，每次讀取一行數據

through2

對node流的二次封裝，更加易於使用

普通用法 through2([ options, ] [ transformFunction ] [, flushFunction ])

• options：{objectMode: true} 等同於through2.obj
• transformFunction(chunk, encode, callback)
• flushFunction 可使2號或者3號參數 每次流傳完能夠和transformFunction同樣作一些數據處理

//將文件中的a所有替換爲z輸出到out.txt
const through2 = require('through2');
const fs = require('fs');

fs.createReadStream('./test/enter.txt')
  .pipe(through2(function (chunk, enc, callback) {
    for (var i = 0; i < chunk.length; i++)
      if (chunk[i] == 97)
        chunk[i] = 122 // swap 'a' for 'z'
 
    this.push(chunk)
 
    callback()
   }))
  .pipe(fs.createWriteStream('./test/out.txt'))
  .on('finish', () => {
      console.log('完事')
  })

through2.obj

const through2 = require('through2');
const csv2 = require('csv2');
const fs = require('fs');

let all = [];
fs.createReadStream('./test/enter.csv')
  .pipe(csv2())
  .pipe(through2.obj(function (chunk, enc, callback) {
    this.push({
        No : chunk[0], 
        activity : chunk[1], 
        time : chunk[2],
        money: chunk[3]
    })
    callback()
  }))
  .on('data', (data)=>{
      all.push(data)
  })
  .on('end', ()=>{
      fs.writeFile('./test/a.js', JSON.stringify(all), ()=>{
        console.log('寫入完成')
      })
  })

through2.ctor對於須要相同處理過程的數據能夠採用該方法建立一個構造函數

let Fc = through2.ctor(function(chunk, enc, callback){
   console.log(chunk)
    for(var i=0;i<chunk.length;i++){
      if(chunk[i]<=97){
        chunk[i] = 98;
      }
    }
    console.log(chunk);
    this.push(chunk);
    callback();
})

fs.createReadStream('./test/enter.txt')
  .pipe(Fc())
  .pipe(fs.createWriteStream('./test/out1.txt'))
  .on('finish', () => {
      console.log('完事')
  })