Learn what immutability is in JavaScript, why it matters, and how modern frameworks like React rely on it for predictable, bug-free code.
了解 JavaScript 中的不可变性是什么、它为何重要，以及 React 等现代框架如何依赖它来实现可预测、无 Bug 的代码。
“Why does my app sometimes behave unpredictably?”
“为什么我的应用有时会出现不可预测的行为？”
If you’ve ever updated an object or array in JavaScript and noticed that another part of your app changed unexpectedly, you’ve run into the consequences of mutable state.
如果你曾在 JavaScript 中更新过一个对象或数组，然后发现应用的另一个部分发生了意外变化，那么你就已经遇到了可变状态带来的后果。
Modern JavaScript frameworks care about immutability because it makes state predictable, prevents hidden bugs, and improves performance.
现代 JavaScript 框架关注不可变性，因为它能让状态变得可预测、防止隐藏的 Bug，并提升性能。
In this article, we’ll cover:
本文涵盖以下内容：
- What immutability really means in JavaScript
不可变性在 JavaScript 中的真正含义 - How mutable vs immutable updates differ
可变更新与不可变更新的区别 - Why frameworks like React rely on immutability
React 等框架为何依赖不可变性 - Best practices for writing immutable code
编写不可变代码的最佳实践
What Is Immutability?
什么是不可变性？
Immutability means values cannot be changed after they are created.
不可变性意味着值在创建之后不能被改变。
Primitive types in JavaScript are immutable:
JavaScript 中的原始类型是不可变的：
let str = "hello";
str.toUpperCase(); // returns "HELLO", does not change original
console.log(str); // "hello"
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