Throw in your token into the client options and give this a try. I think the switch-case was tripping you up.
const twitchjs = require('twitch-js');
const client = new twitchjs.client({
options: { debug: true },
connection: { reconnect: true, secure: true },
identity: { username: 'itsjusttriz', password: '<*HIDDEN*>' },
channels: [ '#itsjusttriz' ]
});
client.on('cheer', (channel, username, userstate, message) => {
client.say(channel, username + ' has cheered ' + userstate.bits + ' bits!');
});