React JS中类型'Readonly <{}>'上不存在属性'currentTime'

Question

I'm trying to use the state variable 'currentTime' in the render() , when i do so i got throwned by error saying "Property 'currentTime' does not exists on type 'Readonly<{}>' "

export class App extends React.Component {

  constructor(props:any){
    super(props);
    this.state = {
     currentTime:(new Date()).toLocaleString()
    }**strong text**
  }

  public setit()
  {
    this.setState(
      {
        currentTime:(new Date()).toLocaleString()
      }
    )
  }

  public render() 
  {
    return (
      <div className="App">
      <h1>Value:{this.state.currentTime}</h1>
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h1 className="App-title">Welcome to React</h1>
        </header>
        <p className="App-intro">
          {this.props.children} <code>src/App.tsx</code> and save to reload.
        </p>`enter code here`
        <input type="button" value="Press" onClick ={this.popup}/>
      </div>
    );
  }
  private popup() : any
  {
    alert("i");
  }
}

export default App;

strong text

Answer 1

I suspect that you forgot to declare an interface for your state.

interface SomeProps {
    otherProps: string
}
interface SomeState {
    currentTime: string
}
class App extends React.Component<SomeProps,SomeState>{
//...
}

Now the state is described as an empty object like this:

class App extends React.Component<{},{}>

Missing interface, typescript doesn't know what to expect.