javascript get parent nested object?

I have an object like this for example:

obj = {
    subobj1: {

    },
    subobj2: {
        func1: function(){

        },
        func2: function(){

        }
    },
    subobj3: {
        func3: function(){

        },
        func4: function(){

        }        
    },
}

How do I call func1 from within func4 without having to call obj.subobj2.func1() ?