Object.freeze是干嘛用的呢？看看API解释的
Prevents the modification of existing property attributes and values, and prevents the addition of new properties.
就是说把一个对象freeze之后就不能修改存在的属性和值了，就是key value都不能修改，而且也不能添加新的属性
// Create an object that has two properties.
var obj = { name: "Nicholas", length: 10 }
// Freeze the object.
Object.freeze(obj)
// Try to add a new property, and then verify that it is not added.
obj.newProp = 50
console.log(obj.newProp) // Ouput: undefined
以上就是要添加一个属性，虽然没有脚本错误提示，但是不成功
// Create an object that has two properties.
var obj = { name: "Nicholas", length: 10 }
// Freeze the object.
Object.freeze(obj)
obj.name = 'Jan'
console.log(obj.name) // Ouput: Nicholas
要修改原有的值，也不成功
并且，StackOverflow上有人说：
There is no way to do this, once an object has been frozen there is no way to unfreeze it.
意思是只要freeze之后，就不能解除了，所以使用这个API需要谨慎
