Slack Incoming Webhooks provide an easy way to post messages to Slack from a PubNub Function.

SlackPost.JS

// FOR A PUBNUB SERVERLESS ENV. 
// Learn More: https://api.slack.com/incoming-webhooks
export default (request, response) => {
    const xhr = require('xhr');
    // Message
    let message = `Hello World!`;
    // Slack Webhook URL
    const url = "SLACK-WEBHOOK-URL-HERE";
    // Basic Slack Post
    const http_options = {
        "headers": {
            "Content-Type": "application/json"
         },
        "method": "POST",
        "body": JSON.stringify({
            "text": message,
        })
    };
    return xhr.fetch(url, http_options).then((x) => {
        //console.log(body);
        return response.send();
    });    
};