merge

-var express = require('express');
-var app = express();
+const express = require('express');
 const config = require('./API_config');
 const config = require('./API_config');
 const line = require('@line/bot-sdk');
 const line = require('@line/bot-sdk');
+const request = require('request');
 
 
-//papago api
-var request = require('request');
+const app = express();
 
 
 //번역 api_url
 //번역 api_url
-var translate_api_url = 'https://openapi.naver.com/v1/papago/n2mt';
+const translate_api_url = 'https://openapi.naver.com/v1/papago/n2mt';
 
 
 //언어감지 api_url
 //언어감지 api_url
-var languagedetect_api_url = 'https://openapi.naver.com/v1/papago/detectLangs';
+const languagedetect_api_url = 'https://openapi.naver.com/v1/papago/detectLangs';
 
 
 // Naver Auth Key
 // Naver Auth Key
 //새로 발급받은 naver papago api id, pw 입력
 //새로 발급받은 naver papago api id, pw 입력
 const client_id = config.client_id;
 const client_id = config.client_id;
 const client_secret = config.client_secret;
 const client_secret = config.client_secret;
 // Line Channel Access Tocken
 // Line Channel Access Tocken
-const line_access = config.line_channel;
+const line_channel = config.line_channel;
 
 
 // create LINE SDK client
 // create LINE SDK client
-const client = new line.Client(line_access);
-
-// create Express app
-// about Express itself: https://expressjs.com/
+const client = new line.Client(line_channel);
 
 
 // ELB health checker
 // ELB health checker
 app.get('/', (req, res) => {
 app.get('/', (req, res) => {
-	console.log('hello,,,,');
+	console.log('ELB health check');
 	res.writeHead(200, { "Content-Type": "text/html" });
 	res.writeHead(200, { "Content-Type": "text/html" });
 	res.end();
 	res.end();
 });
 });
 
 
 // register a webhook handler with middleware
 // register a webhook handler with middleware
 // about the middleware, please refer to doc
 // about the middleware, please refer to doc
-app.post('/webhook', line.middleware(line_access), (req, res) => {
-  Promise
-    .all(req.body.events.map(event => handleEvent(event)))
-    .then((result) => res.json(result))
-    .catch((err) => {
-      console.error(err);
-      res.status(200).end();
+app.post('/webhook', line.middleware(line_channel), (req, res) => {
+	const promises = req.body.events.map(async (event) => {
+		let language_type = await language_detector(event);
+		let options = await option_maker(language_type, event);
+		let result = await receive_result(options, event);
+		client.replyMessage(event.replyToken,result);
+	})
+	Promise
+	.all(promises)
+	.then((result) => res.json(result))
+    	.catch((err) => {
+     	 console.error(err);
+     	 res.status(200).end();
     });
     });
 });
 });
 
 
-// event handler
-function handleEvent(event) {
-  if (event.type !== 'message' || event.message.type !== 'text') {
-    // ignore non-text-message event
-    return Promise.resolve(null);
-  }
-  return new Promise(function(resolve, reject) {
-    //언어 감지 option
-    var detect_options = {
-      url : languagedetect_api_url,
-      form : {'query': event.message.text},
-      headers: {'X-Naver-Client-Id': client_id, 'X-Naver-Client-Secret': client_secret}
-    };
-
-    //papago 언어 감지
-    request.post(detect_options,function(error,response,body){
-      console.log(response.statusCode);
-      if(!error && response.statusCode == 200){
-        var detect_body = JSON.parse(response.body);
-        var source = '';
-        var target = '';
-        var result = { type: 'text', text:''};
-
-        //언어 감지가 제대로 됐는지 확인
-        console.log(detect_body.langCode);
-
-
-        //번역은 한국어->영어 / 영어->한국어만 지원
-        if(detect_body.langCode == 'ko'||detect_body.langCode == 'en'){
-          source = detect_body.langCode == 'ko' ? 'ko':'en';
-          target = source == 'ko' ? 'en':'ko';
-          //papago 번역 option
-          var options = {
-              url:  translate_api_url,
-              // 한국어(source : ko), 영어(target: en), 카톡에서 받는 메시지(text)
-              form: {'source':source, 'target':target, 'text':event.message.text},
-              headers: {'X-Naver-Client-Id': client_id, 'X-Naver-Client-Secret': client_secret}
-          };
-
-          // Naver Post API
-          request.post(options, function(error, response, body){
-              // Translate API Sucess
-              if(!error && response.statusCode == 200){
-                  // JSON
-                  var objBody = JSON.parse(response.body);
-                  // Message 잘 찍히는지 확인
-
-                  result.text = objBody.message.result.translatedText;
-                  console.log(result.text);
-                  //번역된 문장 보내기
-                  client.replyMessage(event.replyToken,result).then(resolve).catch(reject);
-              }
-          });
-        }
-        // 메시지의 언어가 영어 또는 한국어가 아닐 경우
-        else{
-          result.text = '언어를 감지할 수 없습니다. \n 번역 언어는 한글 또는 영어만 가능합니다.';
-          client.replyMessage(event.replyToken,result).then(resolve).catch(reject);
-        } 
-
-      }
-
-    });
-
-    });
-  }
-
+const language_detector = (event) => {
+    if (event.type !== 'message' || event.message.type !== 'text') {
+		// ignore non-text-message event
+		return reject(new Error('메세지 혹은, 텍스트가 아닙니다.'));
+    }
+    return new Promise((resolve) => {
+		//언어 감지 option
+		resolve({
+        	url : languagedetect_api_url,
+			form : {'query': event.message.text},
+			headers: {'X-Naver-Client-Id': client_id, 'X-Naver-Client-Secret': client_secret}
+		});
+    })
+}
+
+const option_maker = (language_type, event) => {
+    return new Promise((resolve, reject) => {
+		request.post(language_type, (error,response) => {
+    	    console.log(response.statusCode);
+        	if(!error && response.statusCode == 200){
+				let detect_body = JSON.parse(response.body);
+				let source = '';
+				let target = '';
+				if (detect_body.langCode == 'ko'||detect_body.langCode =='en'){
+					source = detect_body.langCode =='ko'? 'ko':'en';
+					target = detect_body.langCode =='ko'? 'en':'ko';
+				}
+				//언어 감지가 제대로 됐는지 확인
+				console.log(detect_body.langCode);
+				source = detect_body.langCode;
+
+				var options = {
+					url:  translate_api_url,
+					form: {'source':source, 'target': target, 'text':event.message.text},
+					headers: {'X-Naver-Client-Id': client_id, 'X-Naver-Client-Secret': client_secret}
+				};
+				resolve(options);
+			}
+			else{
+				reject(new Error("request is failed"));
+			}
+		})
+    })
+}
+
+const receive_result = (options, event) => {
+  	return new Promise((resolve, reject) => {
+		var result = { type:'text', text: ''};
+    	request.post(options, (error, response) => {
+      	// Translate API Sucess
+			if(!error && response.statusCode == 200){
+				// JSON
+				var objBody = JSON.parse(response.body);
+				// Message 잘 찍히는지 확인
+				result.text = objBody.message.result.translatedText;
+				console.log(result.text);
+				resolve(result);
+			}
+			else{
+				result.text = '언어를 감지할 수 없습니다. \n 번역 언어는 한글 또는 영어만 가능합니다.';
+				client.replyMessage(event.replyToken,result).then(resolve).catch(reject);
+				reject(new Error("request is failed"));
+			}
+  		})
+	})
+}
 
 
 app.listen(3000, function () {
 app.listen(3000, function () {
   console.log('Linebot listening on port 3000!');
   console.log('Linebot listening on port 3000!');