Really simple Javascript custom event system

event.js

var Event = function() {

    var self = this;

    self.queue = {};
    self.fired = [];

    return {

        fire: function(event) {
            var queue = self.queue[event];

            if (typeof queue === 'undefined') {
                return;
            }

            while (queue.length) {
                (queue.shift())();
            }

            self.fired[event] = true;
        },

        on: function(event, callback) {
            if (self.fired[event] === true) {
                return callback();
            }

            if (typeof self.queue[event] === 'undefined') {
                self.queue[event] = [];
            }

            self.queue[event].push(callback);
        }

    };

}();


// Basic usage

Event.on('counted.to::1000', function() {
    doSomething();
});

for (i = 0; i <= 1000; i++) {
    // Count to 1000...
}

Event.fire('counted.to::1000'); // doSomething() is called

This is really nice, thanks for sharing! Personally I need to setup a system where an callback is called every time an event is fired, so I've modified lines 17-19 to be queue.forEach((callback) => callback()); which works nicely. Thanks for sharing!

Thank you, both @chris-pauley and @wildlyinaccurate. I needed the forEach method Chris shared, but not in es6 mode:

queue.forEach(function (callback) {
    callback();
});

@ttomdewet forEach method is actually supported by IE9+ already. You can use it safely. MDN - forEach

@screets it think he meant the es6 arrow callback...

@wildlyinaccurate thanks a bunch. I think self.fired should be an object self.fired = {}

Very nice piece of code, thanks!

I've moved the
self.fired[event] = true;
line in "fire" to the top of the function. Otherwise, it's not called if fire is called before on (IMHO).

I've also added:
await: async function (event) { // usage (in an async function): await Event.await("counted.to::1000") return new Promise(async function (resolve, rejectUNUSED) { du.eventsQueue.on(event, resolve) }) },