javascript - Redux-form - Redirect after server response

I am using redux-form in react and I would like to redirect to other page after succesful server response ( res 200) . Here is full code with my class LoginForm:

class LoginForm extends React.Component {

  state = {
      redirectToNewPage: false
    }

  handleSubmit=({email='',password=''})=>{
    let error={};
    let isError=false;
    if(email.trim()===''){
      error.email='Required';
      isError=true;
    }   
    if(password.trim()===''){
      error.password='Required';
      isError=true;
    }
    if(isError){
      throw new SubmissionError(error);
      }
    else{
        //this.setState({ redirectToNewPage: true });  // <--- it will redirect
        fetch('/auth', {
          method: 'POST',
          headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json',
          },
          body: JSON.stringify({
            email: email,
            password: password,
          })
        })
        .then( function(res){
          console.log(res.status);
          if(res.status==200){
            console.log("REDIRECTING...");
            //this.setState({ redirectToNewPage: true }); // It will show error unknow function

          }
          else{
            console.log("ERROR");
          }
        })


      }
  }

  static propTypes={
    handleSubmit:React.PropTypes.func
  }

    render(){
      const {handleSubmit}=this.props;
      if (this.state.redirectToNewPage) {
       return (
               
       )
      }
      return(
        

      

        
Login
          
          
        
      
      
    )
}

};

The problem is inside handleSubmit method. I can't use (this.setState()) inside .then after fetch:

.then( function(res){
          console.log(res.status);
          if(res.status==200){
            console.log("REDIRECTING...");
            //this.setState({ redirectToNewPage: true }); // It will show error unknow function

          }
          else{
            console.log("ERROR");
          }

I got an error :

Uncaught (in promise) TypeError: Cannot read property 'setState' of
undefined

Have you got any ideas how to do that?