progressbar is not a function

<div id="demo1" class="mui-text-center">  
    <h5>动态设置进度条进度</h5>  
    <p class="mui-progressbar mui-progressbar-in" data-progress="20"><span></span></p>  
    <ul id="progressbarBtn1" class="mui-pagination">  
        <li><a href="javascript:;" data-progress="10">10%</a></li>  
        <li><a href="javascript:;" data-progress="30">30%</a></li>  
        <li><a href="javascript:;" data-progress="50">50%</a></li>  
        <li><a href="javascript:;" data-progress="100">100%</a></li>  
    </ul>  
</div>

初始化

(function($, doc) {  
    $.init();  
    mui("#demo1").progressbar({progress: 20}).show();  
});

报错 progressbar is not a function 这是为啥？