export default class PlatformEventMonitor extends LightningElement {
    channelName = ‘/event/Sample__e’;
    isSubscribeDisabled = false;
    isUnsubscribeDisabled = !this.isSubscribeDisabled;

    subscription = {};

    // Tracks changes to channelName text field
    handleChannelName(event) {
        this.channelName = event.target.value;
    }

    // Initializes the component
    connectedCallback() {       
        // Register error listener       
        this.registerErrorListener();      
    }

    // Handles subscribe button click
    handleSubscribe() {
        // Callback invoked whenever a new event message is received
        const messageCallback = function(response) {
            console.log(‘New message received: ‘, JSON.stringify(response));
            // Response contains the payload of the new message received
        };

        // Invoke subscribe method of empApi. Pass reference to messageCallback
        subscribe(this.channelName, -1, messageCallback).then(response => {
            // Response contains the subscription information on subscribe call
            console.log(‘Subscription request sent to: ‘, JSON.stringify(response.channel));
            this.subscription = response;
            this.toggleSubscribeButton(true);
        });
    }

    // Handles unsubscribe button click
    handleUnsubscribe() {
        this.toggleSubscribeButton(false);

        // Invoke unsubscribe method of empApi
        unsubscribe(this.subscription, response => {
            console.log(‘unsubscribe() response: ‘, JSON.stringify(response));
            // Response is true for successful unsubscribe
        });
    }

    toggleSubscribeButton(enableSubscribe) {
        this.isSubscribeDisabled = enableSubscribe;
        this.isUnsubscribeDisabled = !enableSubscribe;
    }

    registerErrorListener() {
        // Invoke onError empApi method
        onError(error => {
            console.log(‘Received error from server: ‘, JSON.stringify(error));
            // Error contains the server-side error
        });
    }
}