为什么 React Hook useState 使用 const 而不是 let [英] Why React Hook useState uses const and not let

问题描述

使用 React useState Hook 的标准方法如下:

The standard way to use a React useState Hook is the following:

const [count, setCount] = useState(0);

然而，这个 const count 变量显然会被重新分配给不同的原始值.

However this const count variable is clearly going to be reassigned to a different primitive value.

为什么变量没有定义为let count?

Why then is the variable not defined as let count?

推荐答案

显然将被重新分配给不同的原始值

clearly going to be reassigned to a different primitive value

不是真的.当组件被重新渲染时，函数再次执行，创建一个新的作用域，创建一个新的 count 变量，该变量与之前的变量无关.

Not really. When the component is rerendered, the function is executed again, creating a new scope, creating a new count variable, which has nothing to do with the previous variable.

示例:

let _state;
let _initialized = false;
function useState(initialValue) {
  if (!_initialized) {
    _state = initialValue;
    _initialized = true;
  }
  return [_state, v => _state = v];
}

function Component() {
  const [count, setCount] = useState(0);

  console.log(count);
  setCount(count + 1);
}

Component();
Component(); // in reality `setCount` somehow triggers a rerender, calling Component again
Component(); // another rerender

注意: Hook 更加复杂，实际上并不是这样实现的.这只是为了演示类似的行为.

Note: Hooks are way more sophisticated and are not actually implemented like this. This is just to demonstrate a similar behavior.

这篇关于为什么 React Hook useState 使用 const 而不是 let的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！