Using nodejs to make Slack bot , Slack events not working

I am using one Slack bot library,

https://github.com/blocktrail/slack-tipbot/tree/master/lib

and using this nodejs library ,

var Slack = require('slack-client');

There are 4 events that are working perfect:

slack.on('open', function(e) {});
slack.on('message', function(message) {});
slack.on('close', function(e) {});
slack.on('error', function(error) {});

but when i am trying another event after looking up at slack events API list from url: https://api.slack.com/events-api

and using event like this

 slack.on('member_joined_channel',function(ss){});

its not working

What can be the issue?

via Daniyal Syed