在 TypeScript 中，将类括在尖括号“<>”中是什么意思？
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What does enclosing a class in angle brackets "<>" mean in TypeScript?
提问by davejoem
I am very new to TypeScript and I am loving it a lot, especially how easy it is to do OOP in Javascript. I am however stuck on trying to figure out the semantics when it comes to using angle brackets.
我对 TypeScript 非常陌生，我非常喜欢它，尤其是在 Javascript 中执行 OOP 是多么容易。然而，当涉及到使用尖括号时，我一直试图弄清楚语义。
From their docs, I have seen several example like
从他们的文档中，我看到了几个例子，比如
interface Counter {
(start: number): string;
interval: number;
reset(): void;
}
function getCounter(): Counter {
let counter = <Counter>function (start: number) { };
counter.interval = 123;
counter.reset = function () { };
return counter;
}
and
和
interface Square extends Shape, PenStroke {
sideLength: number;
}
let square = <Square>{};
I am having trouble understanding what this exactly means or the way to think of/understand it.
我无法理解这究竟意味着什么或思考/理解它的方式。
Could someone please explain it to me?
有人可以向我解释一下吗？
回答by Nitzan Tomer
That's called Type Assertionor casting.
这称为类型断言或强制转换。
These are the same:
这些是相同的：
let square = <Square>{};
let square = {} as Square;
Example:
例子：
interface Props {
x: number;
y: number;
name: string;
}
let a = {};
a.x = 3; // error: Property 'x' does not exist on type `{}`
So you can do:
所以你可以这样做：
let a = {} as Props;
a.x = 3;
Or:
或者：
let a = <Props> {};
Which will do the same
哪个会做同样的事情
回答by James Monger
This is called Type Assertion.
这称为类型断言。
You can read about it in Basarat's "TypeScript Deep Dive", or in the official TypeScript handbook.
您可以在Basarat 的“TypeScript Deep Dive”或官方 TypeScript 手册中阅读相关内容。
