const fetch = require('node-fetch');
const fs = require('fs');
const url = 'https://api.upbit.com/v1/market/all?isDetails=false';
const options = {method: 'GET', headers: {Accept: 'application/json'}};

fetch(url, options)
  .then(res => res.json())
  .then(json => {
      var coinName = [];
      var j = 0;
      var file = 'coin_name.txt';
      fs.open(file,'w',function(err,fd){
          if(err) throw err;
      });
      for (i=0;i<json.length;i++) {
        if (json[i].market.indexOf("KRW")>-1){
            console.log(json[i].market);
            coinName[j] = json[i].market;
            j=j+1;
        }
      }
      console.log(coinName);
      fs.writeFile(file,coinName,'utf8',function(error){
        console.log('write end')
      });
    })
  .catch(err => console.error('error:' + err));