联合类型

TypeScript 的类型系统允许您使用各种运算符从现有类型中构建新类型。 现在我们知道如何编写几种类型，是时候开始以有趣的方式组合它们了。

TypeScript's type system allows you to build new types out of existing ones using a large variety of operators. Now that we know how to write a few types, it's time to start combining them in interesting ways.