javascript - React's setState method with prevState argument

Question

I'm new to React, just have a question on setState method. Let's say we have a component:

class MyApp extends React.Component {

  state = {
    count: 3
  };

  Increment = () => {
    this.setState((prevState) => ({
      options: prevState.count + 1)
    }));
  }
}

so why we have to use prevState in the setState method? why can't we just do:

this.setState(() => ({
  options: this.state.count + 1)
}));

Answer 1

Both signatures can be used, the only difference is that if you need to change your state based on the previous state you should use this.setState(function) which will provide you a snapshot(prevState) from the previous state. But if the change does not rely on any other previous value, then a shorter version is recommended this.setState({prop: newValue})

this.setState(prevState =>{
   return{
        ...prevState,
        counter : prevState.counter +1
   }
})

this.setState({counter : 2})