JavaScript类中<{}>的作用是什么？两种组件导出写法有何区别？

Hey there! Let's unpack your questions clearly, since these relate to TypeScript (and how it integrates with React) rather than plain vanilla JavaScript.

First off, vanilla JavaScript doesn't have this <> syntax for classes—this is a TypeScript generic type annotation.

In TypeScript, generics let you create reusable components that work with multiple types instead of a single one. The <{}> here specifically tells TypeScript that the generic parameter (for React components, this is the component's props type) should be an empty object. Think of it as a way to explicitly define: "this component can only accept an empty set of props from its parent."

Let's break down each case, especially since behavior shifts a bit between plain JavaScript and TypeScript:

Case 1: export default class HelloWorldApp extends Component { #

• In plain JavaScript: This is the standard way to export a React class component. There's no type checking here—you can pass any props to the component, and JavaScript won't complain (though React might warn if you pass props the component never uses).
• In TypeScript: React's Component class has default generic parameters where the props type defaults to {} (empty object). So technically, this is equivalent to writing <{}> in most scenarios. That said, omitting the <{}> can make your intent less clear to other developers—they might not immediately realize you're intentionally restricting the component to no props.

Case 2: export default class HelloWorldApp extends Component<{}> { #

• This is strictly a TypeScript-only syntax. By explicitly writing <{}>, you're making it crystal clear that this component expects no props at all. If anyone tries to pass a prop to this component (like <HelloWorldApp message="Hi!" />), TypeScript will throw a compile-time error, catching mistakes early before they cause runtime issues.

The core difference comes down to explicitness in TypeScript: the second version makes your intent (no allowed props) obvious to both the compiler and your team, whereas the first version relies on TypeScript's default behavior.

内容的提问来源于stack exchange，提问作者sadiq