Node js DuplexStream


### Readable & Writable
```typeconst { Duplex } = require("stream")const inoutStream = new Duplex({  write(chunk, encoding, callback) {    console.log(chunk.toString())    callback()  },  read(size) {    this.push(String.fromCharCode(this.currentCharCode++))    if (this.currentCharCode > 90) {      this.push(null)    }  },})inoutStream.currentCharCode = 65process.stdin.pipe(inoutStream).pipe(process.stdout)```
### echo



> [Node.js Stream 당신이 알아야할 모든 것 3편](https://jeonghwan-kim.github.io/node/2017/08/12/node-stream-you-need-to-know-3.html)





