在 TypeScript 中，用尖括号“ < >”括起一个类意味着什么？

我是 TypeScript 的新手，我非常喜欢它，特别是在 Javascript 中做 OOP 是多么容易。然而，当涉及到使用尖括号的时候，我却被困在了试图弄清楚语义的问题上。

从他们的文档中，我看到了几个例子

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;
}

还有

interface Square extends Shape, PenStroke {
sideLength: number;
}
  

let square = <Square>{};

我很难理解这到底是什么意思，或者理解它的方式。

有人能给我解释一下吗？

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小开

This is called Type Assertion.

You can read about it in Basarat's "TypeScript Deep Dive", or in the official TypeScript handbook.

You can also watch this YouTube video for a nice introduction.

小开

最佳答案

That's called Type Assertion or casting.

These are the same:

let square = <Square>{};
let square = {} as Square;

Example:

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:

let a = {} as Props;
a.x = 3;

Or:

let a = <Props> {};

Which will do the same