照着H5+的例子写图片查看页面，加载时出错，ReferenceError: Can't find variable: loadMedia

代码如下

            var url = "view-image.html";  
            show_img_view = plus.webview.create(url,   
                "view-image.html",  
                {scrollIndicator:'none',scalable:true,bounce:"all"});  
            show_img_view.addEventListener("close", function() {  
                show_img_view = null;  
            }, false);  
            show_img_view.addEventListener("loaded", function(){  
                show_img_view.evalJS("loadMedia('"+path+"')");  
            }, false);  
            show_img_view.show("pop-in");

执行时，页面跳转了，但是整个页面都是黑的，log里报错：
[ERROR] : ReferenceError: Can't find variable: loadMedia
file name:pages/view-image.html
line no:1

大神们这种问题怎么解决啊，我小白