TypeScript 3.0 引入了 unknown
类型,根据他们的 wiki:
unknown is now a reserved type name, as it is now a built-in type. Depending on your intended use of unknown, you may want to remove the declaration entirely (favoring the newly introduced unknown type), or rename it to something else.
unknown
和 any
有什么区别?我们什么时候应该使用 unknown
而不是 any
?
最佳答案
您可以在 PR 中阅读更多关于 unknown
的信息或 RC announcement ,但它的要点是:
[..] unknown which is the type-safe counterpart of any. Anything is assignable to unknown, but unknown isn't assignable to anything but itself and any without a type assertion or a control flow based narrowing. Likewise, no operations are permitted on an unknown without first asserting or narrowing to a more specific type.
几个例子:
let vAny: any = 10; // We can assign anything to any
let vUnknown: unknown = 10; // We can assign anything to unknown just like any
let s1: string = vAny; // Any is assignable to anything
let s2: string = vUnknown; // Invalid; we can't assign vUnknown to any other type (without an explicit assertion)
vAny.method(); // Ok; anything goes with any
vUnknown.method(); // Not ok; we don't know anything about this variable
建议的用法是:
There are often times where we want to describe the least-capable type in TypeScript. This is useful for APIs that want to signal “this can be any value, so you must perform some type of checking before you use it”. This forces users to safely introspect returned values.
关于typescript - “未知”与 'any',我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51439843/