移动端Window.prototype后调用不到

Question

我在init.js中
Window.prototype.interface = function(){

return 'https://xxx.xxxxxxx.com'

}
//
Window.prototype.getParam=function(paramName){

var paramValue = "", isFound = !1;
if (this.location.search.indexOf("?") == 0 && this.location.search.indexOf("=") > 1) {
    var arrSource = unescape(this.location.search).substring(1, this.location.search.length).split("&"), i = 0;
    while (i < arrSource.length && !isFound) arrSource[i].indexOf("=") > 0 && arrSource[i].split("=")[0].toLowerCase() == paramName.toLowerCase() && (paramValue = arrSource[i].split("=")[1], isFound = !0), i++
}
return paramValue == "" && (paramValue = null), paramValue

}
给写了两个方法
但是引入init.js以后
页面window.getParam就可以取到值
window.interface就是undefined
请问是什么原因啊

Window.prototype.publicMethod={

interface:'',
getParam:function(){}

}

也一样
请大神解答