Demo Program for Javascript Object Oriented Programming

What will be the output of below Demo Program for Javascript Object Oriented Programming.

<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>

<script>
   var book1 = new book();
   document.getElementById("demo").innerHTML=book1.cover();

   function book(){
     this.cover = cover;
   }

   function cover(){
     return "ecoleather";
   }
</script>

</body>
</html>

 

Save the above program in 1.html and open in a browser. It would give the below output.

ecoleather