如何在mui-bar-transparent背景由透明变为不透明时修改导航栏的字体颜色？

已解决，在mui.min.js里添加如下代码
if((b.scrollY - this.options.top) / this.options.offset > 0.3){
document.getElementById('bartitle').style.color = 'black';
}else{
document.getElementById('bartitle').style.color = 'white';
}
bartitle为导航栏字体span的id。

mui.min.js里源码如下：
function(a, b) {
var c = /^rgba((\d{1,3}),\s(\d{1,3}),\s(\d{1,3}),\s*(\d{1,3}))$/,
d = function(a) {
var b = a.match(c);
return b && 5 === b.length ? [b[1], b[2], b[3], b[4]] : []
},
e = function(b, c) {
this.element = b, this.options = a.extend({
top: 0,
offset: 150,
duration: 16
}, c || {}), this._style = this.element.style, this._bgColor = this._style.backgroundColor;
var e = d(mui.getStyles(this.element, "backgroundColor"));
if(!e.length) throw new Error("元素背景颜色必须为RGBA");
this._R = e[0], this._G = e[1], this._B = e[2], this._A = e[3], this._bufferFn = a.buffer(this.handleScroll, this.options.duration, this), this.initEvent()
};
e.prototype.initEvent = function() {
b.addEventListener("scroll", this._bufferFn), b.addEventListener(a.EVENT_MOVE, this._bufferFn)
}, e.prototype.handleScroll = function() {
this._style.backgroundColor = "rgba(" + this._R + "," + this._G + "," + this._B + "," + (b.scrollY - this.options.top) / this.options.offset + ")"
if((b.scrollY - this.options.top) / this.options.offset > 0.3){
document.getElementById('bartitle').style.color = 'black';
}else{
document.getElementById('bartitle').style.color = 'white';
}
},

//字体跟随导航栏标题同时变色！
function toubuyanse() {
var a111 = getComputedStyle(document.getElementById("header"));
var a222 = a111.background;
var a333 = a222.substring(20, 26);
if(a333 > 0.6 || a333 == "one re") { daohanglan121.style.color = "rgb(230,69,74)"; }//daohanglan121是标题栏H1自己加的id
if(a333 < 0.6 || a333 == "0) non") { daohanglan121.style.color = "white"; }

if(a333 == "one re") { document.getElementById("header").style.borderBottom = "1px solid #eee"; } else {  
    document.getElementById("header").style.borderBottom = "0px solid #eee";  
}  

}
setInterval("toubuyanse()", 300);

Transparent.prototype.handleScroll = function(e) {  
        var y = window.scrollY;  
        if (!this.isNativeScroll && e && e.detail) {  
            y = -e.detail.y;  
        }  
        var opacity = (y - this.options.top) / this.options.offset + this._A;  
        opacity = Math.min(Math.max(this._A, opacity), 1);  
        this._style.backgroundColor = 'rgba(' + this._R + ',' + this._G + ',' + this._B + ',' + opacity + ')';  
        //改变title文字颜色  
        this.element.getElementsByClassName('mui-title')[0].style.color = 'rgba(255,255,255,' + opacity + ')';

发现一个更好的方法，从API中找到，透明度变化时会触发一个alpha自定义事件
$(".mui-bar-transparent").on("alpha", function(evt) {
var alpha= evt.detail.alpha
//当前获得标题栏透明度，而且是变化时触发
});

为什么我的页面滑动的时候没有执行这个方法 也在做这一块 求指导