[Node.JS] 파일 읽기 & 쓰기

const fs = require('fs')

--> 파일 시스템 열때

 

synchronous 

: 동기식 코드 = blocking code 
한줄이 끝나야 다음줄이 실행됨
Single Thread : machine processor 
one application : accessing one thread
아무리 많은 사람들이여도, 같은 application을 다루게되면, 모든 사람이 다른사람들의 실행을 기다렸다가 사용가능함

 

const textInput = fs.readFileSync('./txt/input.txt', 'utf-8');
console.log(textInput);

const textOutput = `This is what we know about the avocado: ${textInput}.\nCreated on ${Date.now()}`
fs.writeFileSync('./txt/output.txt', textOutput)
console.log('File written!');

Non-blocking , asynchronous way
asynchronous : non-blocking code
background에서 실행됨 

 

fs.readFile('./txt/start.txt', 'utf-8', (err, data1) => {
    if (err) return console.log('EROOR!')
    fs.readFile(`./txt/${data1}.txt`, 'utf-8', (err, data2) => {
        console.log(data2);
        fs.readFile("./txt/append.txt", 'utf-8', (err, data3) => {
            console.log("This is data3",data3);
            fs.writeFile('./txt/final.txt',`${data2}\n${data3}`, 'utf-8', err => {
                console.log('Your file has been written');
            })
        });
    });
});