test change tag style using Loop and array

@@ -16,21 +16,7 @@
 
 
 <!--refactoring and conditional statement -->
 <!--refactoring and conditional statement -->
 
 
-  <input id="night_day" type="button" value="night" onclick="
-  if(document.querySelector('#night_day').value==='night')
-  {
 
 
-    var target=document.querySelector('body');
-
-    target.style.backgroundColor= 'black';
-    target.style.color= 'white';
-    document.querySelector('#night_day').value= 'day';
-  }else{
-    target.style.backgroundColor= 'white';
-    target.style.color= 'black';
-    document.querySelector('#night_day').value= 'night';
-  }
-  ">
 <!-- about this grammer
 <!-- about this grammer
 
 
   <input type="button" value="night" onclick="
   <input type="button" value="night" onclick="
@@ -74,7 +60,7 @@
 
 
 
 
 
 
-<!--Loop & Array  -->
+<!--Loop & Array
 <script>
 <script>
   var cowokers=["minsung","leezche","minsoft","sdy"];
   var cowokers=["minsung","leezche","minsoft","sdy"];
 </script>
 </script>
@@ -86,7 +72,62 @@
     i+=1;
     i+=1;
   }
   }
 </script>
 </script>
+-->
+
+<!-- Loop apply
+var alist=document.querySelectorAll('a');
+var i =0;
+while(i<alist.length){
+console.log(alist[i]);
+i+=1;
+}
+-->
+
+<!-- button 1  usage array and Loop for chage style   -->
+<input id="night_day" type="button" value="night" onclick="
+var target=document.querySelector('body');
+if(document.querySelector('#night_day').value==='night')
+{
+  target.style.backgroundColor= 'black';
+  target.style.color= 'white';
+  document.querySelector('#night_day').value= 'day';
+
+  var alist=document.querySelectorAll('a');
+  var i =0;
+  while(i<alist.length)
+  {
+  alist[i].style.color='powderblue';
+  i+=1;
+  }
+}else{
+  target.style.backgroundColor= 'white';
+  target.style.color= 'black';
+  document.querySelector('#night_day').value= 'night';
+
+  var alist=document.querySelectorAll('a');
+  var i =0;
+  while(i<alist.length)
+  {
+  alist[i].style.color='blue';
+  i+=1;
+  }
+}
+">
 
 
+<!-- button2 -->
+  <input id="night_day" type="button" value="night" onclick="
+  var target=document.querySelector('body');
+  if(this.value==='night')
+  {
+    target.style.backgroundColor= 'black';
+    target.style.color= 'white';
+    this.value= 'day';
+  }else{
+    target.style.backgroundColor= 'white';
+    target.style.color= 'black';
+    this.value= 'night';
+  }
+  ">
 
 
   <div id="grid">
   <div id="grid">
     <ol>
     <ol>