A simple javascript event bus

Suteki.EventBus.js

var Suteki = Suteki || {};

Suteki.new_eventBus = (function(){
    var self = {};
    var subscriptions = {};
    var unsubscribeTokens = [];
    var subscriptionPointers = [];

    self.subscribe = function(nameOfMessage, callback){
        var i;
        var subscriptionPointer;
        var unsubscribeToken;

        if(typeof nameOfMessage !== 'string'){
            throw new Error("Suteki.eventBus.subscribe requires a first string argument 'nameOfMessage'");
        }
        if(typeof callback !== 'function'){
            throw new Error("Suteki.eventBus.subscribe requires a second function argument 'callback'")
        }

        if(!subscriptions[nameOfMessage]){
            subscriptions[nameOfMessage] = [];
        }
        subscriptions[nameOfMessage].push(callback);

        // package and return an unsubscribe token.
        subscriptionPointer = { nameOfMessage:nameOfMessage, callbackIndex: subscriptions[nameOfMessage].length-1 };
        i = subscriptionPointers.length;
        unsubscribeToken = {};
        subscriptionPointers[i] = subscriptionPointer;
        unsubscribeTokens[i] = unsubscribeToken;
        return unsubscribeToken;
    };

    self.publish = function(nameOfMessage, data){
        if(typeof nameOfMessage !== 'string'){
            throw new Error("Suteki.eventBus.publish requires a first string argument 'nameOfMessage'");
        }
        if(!data){
            throw new Error("Suteki.eventBus.publish requires a second argument 'data'");
        }

        var i;
        var callback;

        if(subscriptions[nameOfMessage]) {
            for(i=0; i<subscriptions[nameOfMessage].length; i++){
                callback = subscriptions[nameOfMessage][i];
                if(callback){
                    callback(data);
                }
            }
        }
    };

    self.unsubscribe = function(unsubscribeToken){
        var subscriptionPointer = subscriptionPointers[unsubscribeTokens.indexOf(unsubscribeToken)];
        subscriptions[subscriptionPointer.nameOfMessage][subscriptionPointer.callbackIndex] = null;
    };

    return self;
});

// for testing in node
if(exports) {
    exports.new_eventBus = Suteki.new_eventBus;
}

Suteki.EventBusTests.js

// run tests in node

var Suteki = Suteki || {};

Suteki.eventBus = require('./Suteki.EventBus');

Suteki.eventBusTests = (function(new_bus){

    if(!new_bus){
        throw new Error("requires Suteki.EventBus.js");
    }

    var assert = function(passed, message){
        if(!passed){
            console.log("FAILED " + (message || ""))
        };
    };
    var tests = {};

    tests.should_be_able_to_publish_and_subscribe = function(){
        var bus = new_bus();
        var testMessage = "myTestMessage";
        var handler1;
        var handler2;

        bus.subscribe(testMessage, function(data){
            if(data === "Hello World"){
                handler1 = "OK";
            }
        });

        bus.subscribe(testMessage, function(data){
            if(data === "Hello World"){
                handler2 = "OK";
            }
        });

        bus.publish(testMessage, "Hello World");

        assert(handler1 === "OK", "Handler 1 Failed");
        assert(handler2 === "OK", "Handler 2 Failed");
    };

    tests.should_be_able_to_subscribe_and_unsubscribe = function(){
        var bus = new_bus();
        var testMessage = "myTestMessage";
        var resultData = "";

        var unsubscribeToken = bus.subscribe(testMessage, function(data){
            resultData = data;
        });

        bus.publish(testMessage, "Hello");
        assert(resultData === "Hello", "subscription failed");

        bus.unsubscribe(unsubscribeToken);
        bus.publish(testMessage, "No!");
        assert(resultData !== "No!", "unsubscribe failed, callback still present.");
    };

    (function(){
        var testName;
        for(testName in tests){
            if(tests.hasOwnProperty(testName)){
                console.log(">>> " + testName.replace(/_/g, " "));
                tests[testName]();
            }
        }
    }());

}(Suteki.eventBus.new_eventBus));

Run the test in node like this:
node Embassy.EventBusTests.js
should be able to publish and subscribe
should be able to subscribe and unsubscribe