[#3] ボタンのトグル処理を実装

app/assets/javascripts/timer.js

@@ -1,30 +1,27 @@
 document.addEventListener('DOMContentLoaded', function() {
-
         document.getElementById('btn').addEventListener('click', function() {
             toggleBtnFunction();
         })
-
-        document.getElementsByClassName('start-timer').addEventListener('click', function() {
-            startTimer();
-        })
-
-        document.getElementsByClassName('stop-timer').addEventListener('click', function() {
-            stopTimer();
-        })
     }
 )
 
 function toggleBtnFunction() {
     var button = document.getElementById('btn');
-    if(button.value == 'Start') {
+    if(button.value == 'Start' || button.value == 'ReStart') {
         button.value = 'Stop';
         button.className = 'stop-timer';
+        startTimer();
     } else if(button.value == 'Stop') {
-        button.value = 'Start';
+        stopTimer();
+        button.value = 'ReStart';
         button.className = 'start-timer';
     }
 }
 
 function startTimer() {
 
+}
+
+function stopTimer() {
+
 }