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React Communication Between Components

Sending data back to the parent, to do this we simply pass a function as a prop from the parent component to the child component, and the child component calls that function.

In this example, we will change the Parent state by passing a function to the Child component and invoking that function inside the Child component.

import React from 'react';
class Parent extends React.Component {
 constructor(props) {
 this.state = { count: 0 };
 this.outputEvent = this.outputEvent.bind(this);
 outputEvent(event) {
 // the event context comes from the Child
 this.setState({ count: this.state.count++ });
 render() {
 const variable = 5;
 return (
 Count: { this.state.count }
 <Child clickHandler={this.outputEvent} />
class Child extends React.Component {
 render() {
 return (
 <button onClick={this.props.clickHandler}>
 Add One More
export default Parent;

Note that the Parent's outputEvent method (that changes the Parent state) is invoked by the Child's button onClick event.

Not-related Components

The only way if your components does not have a parent-child relationship (or are related but too further such as a grand grand grand son) is to have some kind of a signal that one component subscribes to, and the other writes into.

Those are the 2 basic operations of any event system: subscribe/listen to an event to be notify, and send/trigger/publish/dispatch a event to notify the ones who wants.

There are at least 3 patterns to do that. You can find a comparison here.

Here is a brief summary:

Pattern 1: Event Emitter/Target/Dispatcher: the listeners need to reference the source to subscribe.

to subscribe: otherObject.addEventListener('click', () => { alert('click!'); });
to dispatch: this.dispatchEvent('click');

Pattern 2: Publish/Subscribe: you don't need a specific reference to the source that triggers the event, there is a global object accessible everywhere that handles all the events.

to subscribe: globalBroadcaster.subscribe('click', () => { alert('click!'); });
to dispatch: globalBroadcaster.publish('click');

Pattern 3: Signals: similar to Event Emitter/Target/Dispatcher but you don't use any random strings here. Each object that could emit events needs to have a specific property with that name. This way, you know exactly what events can an object emit.

to subscribe: otherObject.clicked.add( () => { alert('click'); });
to dispatch: this.clicked.dispatch();


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