经典的发布订阅者模式

function Pubsub() {
    this.handlers = {};
}
Pubsub.prototype = {
    on: function (eventType, handler) {
        var self = this;
        if (!(eventType in self.handlers)) {
            self.handlers[eventType] = [];
        }
        self.handlers[eventType].push(handler)
    },
    emit: function (eventType) {
        var self = this;
        var handlerArgs = Array.prototype.slice.call(arguments, 1);
        for (var i = 0; i < self.handlers[eventType].length; i++) {
            self.handlers[eventType][i].apply(self, handlerArgs)
        }
        return self;
    },
    off: function (eventType, handler) {
        var currentEvent = this.handlers[eventType];
        var len = 0;
        if (currentEvent) {
            len = currentEvent.length;
            for (var i = len - 1; i >= 0; i--) {
                if (currentEvent[i] === handler) {
                    currentEvent.splice(i, 1)
                }
            }
        }
        return this;
    }
}

var pubsub = new Pubsub();
var callback = function (data) {
    console.log(data)
}
pubsub.on('A', function (data) {
    console.log(data + 1)
})
pubsub.on('A', function (data) {
    console.log(data + 2)
})
pubsub.on('A', callback)
pubsub.emit('A', '参数')
pubsub.off('A', callback)
pubsub.emit('A', '二参数')