PhantomJS onClosing()

var wpage = require('webpage').create(); 
wpage.onClosing = function(str) {}

var wpage = require('webpage').create(); 
wpage.onClosing = function(str) { 
   console.log("page is closed"); 
} 
wpage.open('http://localhost/tasks/closing.html', function(status) { 
   console.log(status); 
   wpage.close();   
});

success 
page is closed