JavaScript对象的对象中如何互相取值？

Question

http://jsbin.com/qeleboyeme/1/edit?js,console
vara={
apple:{
apple1:"ap1",
apple2:"ap2"
},
banana:{
banana1:"ba1",
banana2:"ba2",
//banana3:a.apple.apple1,
banana4:this.banana1,
},
pear:function(){
console.log(this.banana.banana1);
}
};
console.log(a.banana.banana1);
console.log(a.banana.banana2);
console.log(a.banana.banana3);
console.log(a.banana.banana4);
a.pear();
//a.banana想取a.apple里面的值怎么办？
如题，a.banana想取a.apple里面的值怎么办？pear中的this指向的是a，banana4中的this指向的是global
如果把banana3那里的注释去掉会直接报错