Используя подсказку реактивного маршрутизатора в componentWillUnmount

  **//APP.js**


import React from 'react';

class App extends Component{
  state  = {
   data = []// array of data
  }

 render(){
  return(
   <div>
    <CustomForm 
     data = {this.state.data}
    />
   </div>
 )
 }
}

export default App


**//CustomForm.js**

import React from 'react';
import {connect} from 'react-redux';
import CustomField from './CustomField';
import { Field, reduxForm } from 'redux-form';
import {Prompt} from 'react-router'    
 
class CustomForm extends Component{

 state  = {
  formChanged: false
 }
 
 onSubmit = (values) => {
   console.info(values)
 }
 
 componentWillUnmount(){
   if (this.props.dirty){
     this.setState({
      formChanged: true
     })
   }
 }

 render(){
  return(
   <div>
   {
    this.state.formChanged?
     <Prompt 
      when = {shouldBlockNavigation}
      message='You have unsaved changes, are you sure you want to leave?'
      />
      :
      null
    }
    <Form  onSubmit = {handleSubmit(this.onSubmit)}>
     <Field                                                    
      name = "field1"                                            
      type = "text"                                              
      component = {CustomField}
      label = "field1"
     />
    </Form>
   </div>
 )
 }
}

export default reduxForm({
  form: "NewForm",
  destroyOnUnmount: true,
  forceUnregisterOnUnmount: false 
})(connect(mapStateToProps, mapDispatchToProps)(CustomForm))