SOURCE

//实现事件的发布-订阅
function Events() {
    this.events = {};
}
Events.prototype = {
    constructor: Events,
    on: function(eventType, callback) {
        if (!this.events[eventType]) {
            this.events[eventType] = [];
        }
        this.events[eventType].push(callback);
        return this;
    },
    remove: function(eventType) {
        for (var key in this.events) {
            if (this.events.hasOwnProperty(key) && key === eventType) {
                delete this.events[eventType];
            }
        }
    },
    emit: function(eventType) {
        if (!this.events[eventType]) {
            return this;
        }
        var args = Array.prototype.slice.call(arguments, 1);
        for (var i = 0; i < this.events[eventType].length; i++) {
            this.events[eventType][i].apply(this, args);
        }
        return this;
    }
}