为什么JS允许对象属性既“引用”又不引用？有区别吗？

Question

为什么JS允许对象属性同时为"quoted"和non-quoted？有区别吗？

var object = {

    "firstName": "SpongeBob", //quoted
    lastName: "SquarePants"   //non-quoted

};

console.log(object.firstName); // -> SpongeBob
console.log(object.lastName);  // -> SquarePants

Answer 1

当然有：

var obj = {
    "crazy-property!name": "some string"
    // crazy-property!name is an invalid property name without quotation marks
};

console.log(obj["crazy-property!name"]);
// can't do console.log(obj.crazy-property!name)