为什么在使用JavaScript定义后可以更改对象const？ [英] Why object const can be changed after definition in JavaScript?

问题描述

在JavaScript中：

In JavaScript:

const a = 6;
a = 2; // Error

const o = {};
o = 7; // Error
o.a = 5; // Good. Why?

const o = {a:1};
o.a = 2; // Good. Why?

我发现人们有时会定义const对象，但后来更改了它的值。为什么在定义后可以更改const？

I found people sometimes define a const object but later change its value. Why a const can be changed after its definition?

推荐答案

用 const 表示一件事：独立变量名称以后不能用 = 重新分配。

A variable declared with const means one thing: the standalone variable name cannot be reassigned with = later.

相反， oa = 5; 并未重新分配变量名称-它是在改变对象的内容，但并未更改 o 变量指向内存中。

In contrast, o.a = 5; is not reassigning the variable name - it's mutating the content of the object, but it's not changing what the o variable points to in memory.

防止变量名重新分配 ，请使用 const 。要防止对象的变异是完全不同的-为此，您需要类似 Object.freeze 或使用 immutable-js 。

To prevent reassignment of a variable name, use const. To prevent mutation of an object is something entirely different - for that, you'd need something like Object.freeze or manipulate objects using immutable-js.

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