test how to convey parameter by self

@@ -7,11 +7,11 @@
 <script>
 function nightDayHandler(self){
     var target=document.querySelector('body');
-    if(this.value==='night')
+    if(self.value==='night')
     {
       target.style.backgroundColor= 'black';
       target.style.color= 'white';
-      this.value= 'day';
+      self.value= 'day';
 
       var alist=document.querySelectorAll('a');
       var i =0;
@@ -23,7 +23,7 @@ function nightDayHandler(self){
     }else{
       target.style.backgroundColor= 'white';
       target.style.color= 'black';
-      this.value= 'night';
+      self.value= 'night';
 
       var alist=document.querySelectorAll('a');
       var i =0;