类型反应打字稿上不存在属性

Question

I'm a newbie in typescript, could anyone please tell me why do I get this error?

Property 'interval' does not exist on type 'App'.

interface State {
  userInput:string[];
  secondsPassed:number;
  }


class App extends React.Component<any, State>{
    state:State = {
      userInput:[],
      secondsPassed:0
    }
  startTimer = () => {
      this.interval = setInterval( () => {
        this.setState(() =>{
          return {secondsPassed: this.state.secondsPassed+1}
        })
      },1000)
    
  }

Answer 1

Try something like this:

 const interval = setInterval(() => {
    this.setState(() =>{
          return {secondsPassed: this.state.secondsPassed+1}
        })
      },1000)

Answer 2

Typescript is a statically-typed language. Part of that means you have to declare the variables of a class before its assignment. Simply declare interval as in the following:

class App extends React.Component<any, State>{
  interval

  state:State = {
    userInput:[],
    secondsPassed:0
  }
  startTimer = () => {
    this.interval = setInterval( () => {
      this.setState(() =>{
        return {secondsPassed: this.state.secondsPassed+1}
      })
    },1000)

  }

Answer 3

The first answer got it close, the solution looks like this:

 class App extends React.Component<any, State>{
      private interval: any ;
        state:State = {
          userInput:[],
          secondsPassed:0
        }
      startTimer = () => {
          this.interval = setInterval( () => {
            this.setState(() =>{
              return {secondsPassed: this.state.secondsPassed+1}
            })
          },1000)
        
      }