Sharing store change event between same hierarchical level child components

Question

I am developing a simple React JS application for learning purpose. I just started learning React JS a few days ago. Now, I am having a problem with Flux Store. I need to share the change event across two child components on the same hierarchical level.

I have the parent component, called TodoComponent with the following definition

//Create
class TodoComponent extends React.Component{
    constructor(props){
        super(props)

    }


    render(){

        return (
            <div>
                <div>
                <ListComponent />
                </div>
                <AddItemComponent />
            </div>
        )
    }
}

It has two child components called, ListComponent and the AddItemComponent. Moreover, I have a store with this definition.

import { EventEmitter } from 'events';

class DataStore extends EventEmitter{

    constructor()
    {
        super();
        this.todos = [
            "Eat",
            "Sleep",
            "Die",
            "Shower"
        ];
    }

    getAll(){
        return this.todos;
    }

    addItem(newItem)
    {
        this.todos.push(newItem);
        this.emit("change")
    }

}

const dataStore = new DataStore;

export default dataStore;

It has a function for adding new item into the array and a function for fetching the array.

This is the ListComponent that is displaying the array of items from the DataStore flux store.

import React from 'react';
import TodoItem from './TodoItem';
import DataStore from './data.store';

class ListComponent extends React.Component{
    constructor(props)
    {
        super(props)
        this.state = { todos : DataStore.getAll() };
    }

    componentWillMount(){
        DataStore.on('change', () => {
            //do somethif
            this.state = { todos : DataStore.getAll() };
        })
    }

    render()
    {
        var deleteItem = (item) => {
            this.deleteItem(item);
        }
        var editItem = (item) => {
            this.editItem(item);
        }

        var addItem = (newItem) => {
            this.addItem(newItem);
        }
        var todos = this.state.todos.map((item, index) => {
            return (
                <TodoItem item={item} addItem={addItem.bind(this)} deleteItem={deleteItem} editItem={editItem} />
            )
        });

        return (
            <ul>
                {todos}
            </ul>
        )
    }

    deleteItem(item)
    {
        this.setState({ todos: this.state.todos.filter((listItem, index) => {
            return listItem !== item; 
        }) });
    }

    editItem(item)
    {
        alert(item)
    }

    addItem(newItem)
    {
        DataStore.addItem(newItem);
    }
}

module.exports = ListComponent;

It is updating the items in the change event of the DataStore store. But I am not calling the addItem function in the ListComponent. I am calling it in the AddItemComponent. This is the definition of the AddItemComponent.

import React from 'react';
import DataStore from './data.store';

class AddItemComponent extends React.Component{
    constructor(props)
    {
        super(props)

    }

    render()
    {
        return (
            <form id="form-todo" onSubmit={this.addItem.bind(this)} action="post">
                <input type='text' ref="newItem" />
                <button>ADD</button>
            </form>
        );
    }

    addItem(e)
    {
        e.preventDefault();
        DataStore.addItem(this.refs.newItem.value);
    }
}

module.exports = AddItemComponent;  

But when I trigger the addItem function in the AddItemComponent, the change event of the DataStore in the ListComponent is not triggered. Therefore, how can I synchronize the change event of Flux Store between two components exist on the same hierarchical level?

The solution I can think of is having the DataStore in the TodoComponent (parent component) and send the data and functions as props to the child component. I think, the code will become a bit messy in that way. Is that the only solution to do that?

Answer 1

Welcome to React! I recreated your example and your "change" event is firing in ListComponent, but to update the state in a component you should use this.setState(changes) rather than this.state = {changes}. Only use this.state = {} in the constructor to set the initial state. The setState method properly flows through the React lifecycle and causes the component to re-render using the new state. There is an official guide on React's state and lifecycle hooks here.