typescript 中的语法是什么？

Question

    type JSXElementConstructor<P> =
        | ((props: P) => ReactElement<any, any> | null)
        | (new (props: P) => Component<any, any>);       => What is this?

It seems it's trying to define a method signature but then what how is it different from the way the line above describes a method?

Answer 1

((props: P) => ReactElement<any, any> | null) describes a plain function that, when called, returns a ReactElement.

(new (props: P) => Component<any, any>) describes a class that, when called with new , returns a Component - hence the new .

They're not interchangeable. The union lets JSXElementConstructor account for both functional components and class components.

For a simple example outside of React of a newable that's assignable to new () => :

type X = (new () => { getName: () => string });
class Person {
    #name = 'foo';
    getName() {
        return this.#name;
    }
}

const P: X = Person;