React JS Event-Emitter Mixin and Example

app.js

var React = require("react"), Dom = React.DOM;
var LogOutButton = require('./src/logout');
var events = require('api/events');

var Main = React.createClass({
    // this mixin provides this.emitLogout, and if we set onLogout it'll be called when "logout" is emitted
    mixins: [events.mixinFor("logout")],

    getInitialState: function(){
        return {
            user: null
        };
    },
    logIn: function(){
        this.setState({
            user: {name: "foobar"}
        });
    },

    // update our state when the login event is emitted
    onLogout: function(){
        this.setState({
            user: null
        });  
    },
    render: function() {
        var user = this.state.user;

        return Dom.div(null, 
            user && Dom.span(null, "Hi " + user.name),
            user && LogOutButton(),
            !user && Dom.button({onClick: this.logIn},
            "log in")
        );
    }
});

React.renderComponent(Main(), document.body);

logout.js

var React = require("react"), Dom = React.DOM;
var events = require('api/events');

var Logout = React.createClass({
    mixins: [events.mixinFor("logout")],
    render: function() {
        window.x = this

        // directly bind our event to a button click event
        return Dom.button({
            onClick: this.emitLogout
        }, 'log out');
    }
});

module.exports = Logout;

react-event-emitter.js

var EventEmitter = require('events').EventEmitter;
var globalEmitter = module.exports = new EventEmitter();

module.exports.mixinFor = function (eventName, events) {
    events = events || globalEmitter;

    // "fooBar" => "FooBar"
    var pascal = eventName[0].toUpperCase() 
                      + eventName.slice(1);

    var noop = function(){};

    var mixin = {
        componentWillMount: function(){
            if (!this["on" + pascal]) {
                return;
            }

            events.on(event, this["on" + pascal]);
        },
        componentWillUnmount: function(){
            if (!this["on" + pascal]) {
                return;
            }

            events.off(event, this["on" + pascal]);
        }
    };

    // add emit method
    mixin["emit" + pascal] = 
        events.emit.bind(events, event);

    return mixin;
};

Sorry, what does this LINE stand for?