React.js - Communicate Between Components

Communication between Stateless Functional Components

In this example we will make use of Redux and React Redux modules to handle our application state and for auto re-render of our functional components.,

In the example below we have three different components and one connected component

• UserInputForm: This component display an input field And when the field value changes, it calls inputChange method on props (which is provided by the parent component) and if the data is provided as well, it displays that in the input field.

• UserDashboard: This component displays a simple message and also nests UserInputForm component, It also passes inputChange method to UserInputForm component, UserInputForm component inturn makes use of this method to communicate with the parent component.

UserDashboardConnected : This component just wraps the UserDashboard component using ReactRedux connect method., This makes it easier for us to manage the component state and update the component when the state changes.

• App: This component just renders the UserDashboardConnected component.

const UserInputForm = (props) => {
  let handleSubmit = (e) => {
    e.preventDefault();
  }

  return(
    <form action="" onSubmit={handleSubmit}>
      <label htmlFor="name">Please enter your name</label>
      <br />
      <input type="text" id="name" defaultValue={props.data.name || ''} onChange={ props.inputChange } />
    </form>
  )
}


const UserDashboard = (props) => {
  let inputChangeHandler = (event) => {
    props.updateName(event.target.value);
  }

  return(
    <div>
      <h1>Hi { props.user.name || 'User' }</h1>
      <UserInputForm data={props.user} inputChange={inputChangeHandler} />
    </div>
  )
}

const mapStateToProps = (state) => {
  return {
    user: state
  };
}
const mapDispatchToProps = (dispatch) => {
  return {
    updateName: (data) => dispatch( Action.updateName(data) ),
  };
};

const { connect, Provider } = ReactRedux;
const UserDashboardConnected = connect(
  mapStateToProps,
  mapDispatchToProps
)(UserDashboard);

const App = (props) => {
  return(
    <div>
      <h1>Communication between Stateless Functional Components</h1>
      <UserDashboardConnected />
    </div>
  )
}

const user = (state={name: 'John'}, action) => {
  switch (action.type) {
    case 'UPDATE_NAME':
      return Object.assign( {}, state, {name: action.payload}  );

    default:
      return state;
  }
};

const { createStore } = Redux;
const store = createStore(user);
const Action = {
  updateName: (data) => {
    return { type : 'UPDATE_NAME', payload: data }
  },
}


ReactDOM.render(
  <Provider store={ store }>
    <App />
  </Provider>,
  document.getElementById('application')
);

Output :

There are a total of 3 cases of communication between React components:

• Case 1: Parent to Child communication
• Case 2: Child to Parent communication
• Case 3: Not-related components (any component to any component) communication

Examples

Parent to Child Components

That the easiest case actually, very natural in the React world and the chances are - you are already using it.

You can pass props down to child components. In this example message is the prop that we pass down to the child component, the name message is chosen arbitrarily, you can name it anything you want.

import React from 'react';

class Parent extends React.Component {
    render() {
        const variable = 5;
        return (
            <div>
                <Child message="message for child" />
                <Child message={variable} />
            </div>
        );
    }
}
class Child extends React.Component {
    render() {
        return <h1>{this.props.message}</h1>
    }
}
export default Parent;

Here, the <Parent /> component renders two <Child /> components, passing message for child inside the first component and 5 inside the second one.

In summary, you have a component (parent) that renders another one (child) and passes to it some props.

Child to Parent 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) {
        super(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 (
            <div>
                Count: { this.state.count }
                <Child clickHandler={this.outputEvent} />
            </div>
        );
    }
}

class Child extends React.Component {
    render() {
        return (
            <button onClick={this.props.clickHandler}>
                Add One More
            </button>
        );
    }
}
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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