如何从闭包中获得变量

function foo(){
    var person = {
        "name": "joe",
        "age": 18
    }
    return function getValue(name){
        return person[name];
    }
};
var bar = foo();
bar('name'); //=> 'joe'
Object.defineProperty(Object.prototype, 'self', {
    get: function() {
        return this;
    }
});
bar('self'); //=> {name": "joe", "age": 18}