Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
<script id="jsbin-javascript">
function counter( start ) {
  this.count = start;

  this.increase = function() {
    return this.count++;
  }

  this.decrease = function() {
    return this.count--;
  }

  this.display = function() {
    console.log( this.count );
  }
}


var a = new counter( 0 );
var b = new counter( 2 );
var c = new counter( 12 );
a.increase();
a.increase();
a.increase();
a.display();

b.decrease();
b.decrease();
b.decrease();
b.display();

c.increase();
c.display();
</script>
</body>
</html>