What does the error “JSX element type '…'

问题:

I wrote some code:

function renderGreeting(Elem: React.Component<any, any>) {
    return <span>Hello, <Elem />!</span>;
}

I'm getting an error:

JSX element type Elem does not have any construct or call signatures

What does it mean?

回答1:

This is a confusion between constructors and instances.

Remember that when you write a component in React:

class Greeter extends React.Component<any, any> {
    render() {
        return <div>Hello, {this.props.whoToGreet}</div>;
    }
}

You use it this way:

return <Greeter whoToGreet='world' />;

You don't use it this way:

let Greet = new Greeter();
return <Greet whoToGreet='world' />;

In the first example, we're passing around Greeter, the constructor function for our component. That's the correct usage. In the second example, we're passing around an instance of Greeter. That's incorrect, and will fail at runtime with an error like "Object is not a function".

---

The problem with this code

function renderGreeting(Elem: React.Component<any, any>) {
    return <span>Hello, <Elem />!</span>;
}

is that it's expecting an instance of React.Component. What you want a function that takes a constructor for React.Component:

function renderGreeting(Elem: new() => React.Component<any, any>) {
    return <span>Hello, <Elem />!</span>;
}

or similarly:

function renderGreeting(Elem: typeof React.Component) {
    return <span>Hello, <Elem />!</span>;
}

回答2:

If you want to take a component class as a parameter (vs an instance), use React.ComponentClass:

function renderGreeting(Elem: React.ComponentClass<any>) {
    return <span>Hello, <Elem />!</span>;
}

回答3:

When I'm converting from JSX to TSX and we keep some libraries as js/jsx and convert others to ts/tsx I almost always forget to change the js/jsx import statements in the TSX\TS files from

import * as ComponentName from "ComponentName";

to

import ComponentName from "ComponentName";

If calling an old JSX (React.createClass) style component from TSX, then use

var ComponentName = require("ComponentName")

回答4:

If you really don't care about props then the widest possible type is React.ReactType.

This would allow passing native dom elements as string. React.ReactType covers all of these:

renderGreeting('button');
renderGreeting(() => 'Hello, World!');
renderGreeting(class Foo extends React.Component {
   render() {
      return 'Hello, World!'
   }
});

回答5:

If you are using material-ui, go to type definition of the component, which is being underlined by TypeScript. Most likely you will see something like this

export { default } from './ComponentName';

You have 2 options to resolve the error:

1.Add .default when using the component in JSX:

import ComponentName from './ComponentName'

const Component = () => <ComponentName.default />

2.Rename the component, which is being exported as "default", when importing:

import { default as ComponentName } from './ComponentName'

const Component = () => <ComponentName />

This way you don't need to specify .default every time you use the component.