范围问题与fadeIn的序列有关

function Sequence() {
    var sequence = [];
    var pos = 0;

    Sequence.prototype.add = function(obj) {
        sequence.push(obj);
    };

    Sequence.prototype.start = function() {
        sequence[pos].run();
    };

    Sequence.prototype.next = function() {
        pos++;
        sequence[pos].run();
    }; 
};

function fadeIn(params) {
    this.id = params.id;
    this.onComplete = params.onComplete;

    var self = this;
    var timer;
    var i = params.opacity;

    fadeIn.prototype.run = function(){
        timer = setInterval(function() {
            params.element.style.opacity = i / 10;
            i++;

            if (i / 10 == 1) {
                clearInterval(timer);
                self.onComplete();
            }
        }, params.fps);
    }
};

var sequence = new Sequence();
var fader = document.getElementById(\'fader1\');
var items = fader.getElementsByTagName(\"li\");

sequence.add(new fadeIn({
    \"id\": \"instance_0\",
    \"element\": items[0],
    \"opacity\": 0,
    \"fps\": 80,
    \"onComplete\": function() {
        sequence.next();
    }
}));

sequence.add(new fadeIn({
    \"id\": \"instance_1\",
    \"element\": items[1],
    \"opacity\": 0,
    \"fps\": 80,
    \"onComplete\": function() {
        sequence.next();
    }
}));

sequence.start();