how to write the prevState in react code example

Example 1: react prevstate

handleClick() {
  this.setState(prevState => ({
    isToggleOn: !prevState.isToggleOn
  }));
}

Example 2: prevstate in react

handleClick() {
        this.setState(prevState => {
            return {
                count: prevState.count + 1
            }
        })
    }