javascript - 为什么常数字段不 protected ？

Question

const 可用于声明常量:

> const a = 42
undefined
> a = 7
7
> a
42

这很酷，但我观察到，当使用 const 声明对象时，此行为不再起作用:

> const b = { foo: { bar: 42 }, baz: 7 }
undefined
> b.baz = { hello: "world" }
{ hello: 'world' }
> b.foo.bar = 7
7
> b
{ foo: { bar: 7 }, baz: { hello: 'world' } }

如您所见，我将 baz 字段修改为对象，并将 42 更改为 7。

阅读docs我看到这是预期的:

// Overwriting the object fails as above (in Firefox and Chrome
but not in Safari)
MY_OBJECT = {"OTHER_KEY": "value"};

// However, object attributes are not protected,
// so the following statement is executed without problems
MY_OBJECT.key = "otherValue";

但是，为什么会这样呢？背后的逻辑是什么？

另一方面，问题是:如何声明常量对象？

Answer 1

However, why this is working like this? What is the logic behind?

const 只是将绑定(bind)声明为常量。它不会自动使其初始化的每个值都是不可变的。

how to declare constant objects?

要防止对象发生变异，您可以 Object.freeze它:

"use strict";
const b = Object.freeze({foo: Object.freeze({bar: 42}), baz: 7});
b.baz = {hello: "world"}; // Error: Invalid assignment in strict mode