因此，我最近在Reaction Native中切换到来自Java脚本的TypeScrip，在输入判断useNavigation钩子时遇到了一个问题.
const nav: typechecking = useNavigation()
和
const nav = useNavigation<typechecking>()
它们都适用于我的代码，但我在想它们之间的区别？
但是，对此的正确解释是什么呢？
Like, what i could think was that because useNavigation() hook could have many return types, we have restricted he return type to typechecking in the 2nd one.
While in the 1st one, we are receiving all the types from useNavigation() hook but are checking nav for typechecking only.
TLDR没有什么不同.
下面是一张explicit type annotation.您告诉编译器nav有一个指定的类型typechecking(您通常希望用大写来编写类型).
const nav: typechecking = useNavigation()
这没有显式的类型注释，nav的类型由编译器根据useNavigation<typechecking>()的返回类型自动推断.相反，您将一个泛型参数传递给函数，该参数可能会影响它的返回类型，具体取决于函数声明.
const nav = useNavigation<typechecking>()
我们可以通过看一看宣言(source code on Github)来证实这一假设.您将看到该函数返回泛型参数T.
export function useNavigation<
T = NavigationProp<ReactNavigation.RootParamList>
>(): T {
// implementation
}
如上所述，现在将根据您作为泛型参数传递的useNavigation()的返回类型自动推断nav的类型.