Borrowed from Contra and applied to an angular module

Contra.eventEmitter.js

angular.module('contra.eventEmitter', [])
    .factory('eventEmitter', function () {
    'use strict';

    return {
        emitter: function (thing) {
            var evt = {},
                tick = function tick (fn) { setTimeout(fn, 0); },
                debounce = function (fn, args) { if (!fn) { return; } tick(function run () { fn.apply(null, args || []); }); }
            if (thing === undefined) { thing = {}; }
            thing.on = function (type, fn) {
                if (!evt[type]) {
                    evt[type] = [fn];
                } else {
                    evt[type].push(fn);
                }
            };
            thing.once = function (type, fn) {
                fn._once = true; // thing.off(fn) still works!
                thing.on(type, fn);
            };
            thing.off = function (type, fn) {
                var et = evt[type];
                if (!et) { return; }
                et.splice(et.indexOf(fn), 1);
            };
            thing.emit = function () {
                var args = Array.prototype.slice.call(arguments),
                    type = args.shift(),
                    et = evt[type];

                if (type === 'error' && !et) { throw args.length === 1 ? args[0] : args; }
                if (!et) { return; }
                evt[type] = et.filter(function emitter (listen) {
                    debounce(listen, args);
                    return !listen._once;
                });
            };
            return thing;
        }
    };
});