Javascript: Hack object to return a default value insteadof unknown when accessing not exist properity

Question

I know that this feal crazy but is there a way to return a value when accessing not exist property of an object in Javascript
For example

function Func(){
        this.msg='hello'
}
var obj= new Func();
alert(obj.msg) // hello
alert(obj.foo) // undefined

Are there a way for obj.foo to return a defult value not undefined rather than alert(obj.hasOwnProperty('foo'):obj.foo||'foo')