Javascript wrong use of this in OOP

wrong use of this

// Main Class Foo
function foo(){
	// Foo has some properties we need to access later
	this.test = "hello scope";
	// We call a member function on a timer
	setTimeout( this.bar, 1000 );
}
foo.prototype.bar = function(){
	// once the timer is called it executes this function
	// but as a result of using the timer we have lost our referenced parent
	// this now becomes the document
	// outputting this will return
	// Window 127.0.0.1 ( assuming you run on your local box
	alert( this );
	// thus trying to access this.test will result in trying to access 
	// the global variable called test or in other words window.test 
	// which is different than our foo.test 
	// ( assuming window.test wasn't already defined somewhere else )
	alert( this.test );
}
var x = new foo();